* Add styled-components dependency to start introducing it to components instead of Sass

* Wrap App.js with styled-components ThemeProvider and inject `fetherTheme` prop colours so they are available to child components.

* Added styled-components' GlobalStyle https://www.styled-components.com/docs/faqs boilerplate as child of ThemeProvider so global styles may be defined here

* Replace assets/sass/layouts/_wrapper.scss with styled-components including:
  * DivContent is declared in App.js since it is only used here
  * DivWindow is declared in App.js since it is only used here
  * DivWindowContent is declared in shared folder since used by different components

* Removed assets/sass/layouts/_wrapper.scss. Noting that `.connector` class is not used

* Use styled-components in TxForm and TxDetails components (that were introduced in PR #307).

* Add a style.js file in the same directory of the component where styled-components are used

* Add styled-components theme animations folder with a SlideInLeft animation and introduce a theme to TxDetails

* Add keyframes animation to TxDetails component (i.e. slide-in animation that's used in the details section that appears when you click Details/Hide button on the Send Ether/THIBCoin page)

* Fix `faint` style implementation to use `rgba` with styled-components

* Note that I decided not to use defaultProps feature of styled-components as it bloats the code too much

* Note that currently we are using Sass _variables.scss for colour variables, and since many components still use some of the Sass variables we cannot remove them yet.

* Note that the original branch where this work was done is https://github.com/paritytech/fether/compare/luke-293-show-tx-fee-styled-components?expand=1, but since multiple PRs have since been merged it was easier to just code again using it as reference

* Disadvantage of styled-components appears to be when you go to debug components in Dev Tools > Elements. The classNames appear as a hash `<div class="sc-EHOje dGUdfn">` instead of the classname!!

- Add option to import a Parity Signer account. It is then stored in
local storage.

- Send transactions with Parity Signer accounts

- Refactor sendStore so that "token" (and chainId) is inside this.tx;
avoids having to pass `token` around every function, and it makes sense
to put it in the object since it is part of the tx info.

- Add account type (either node or signer) to accountsInfo

- Add account type to withAccount; output props are now `{account:
{address, type}}` instead of `{accountAddress}`

* Move toggle details buttons and associated methods and showDetails state into nav of TxForm component

* Pass showDetails down as props to TxDetails

* Remove previous attempt to display TxDetails like a popup above other fields
(i.e. remove form-details-wrapper and -details-value styles)

* Move "Details" / "Hide" buttons into the form-nav footer section

* TxDetails now appears above the footer area above other input fields without causing the screen height to increase

* Background of the TxDetails darkened so it stands out from surroudings

* Change "Details" arrow to point upwards since TxDetails now shown above

* Change "Hide" arrow to point downward since TxDetails now shown above

* Rename classnames to `_` or `-` more consistently

* Note: To quickly display the 'Details' button so you can click it change TxForm.js as follows:

```
{/* {valid && this.estimatedTxFee(values) ? ( */}
  <TxDetails
    // estimatedTxFee={this.estimatedTxFee(values)}
    estimatedTxFee={new BigNumber('8100000')}
    token={token}
    // values={values}
    values={ { amount: new BigNumber('0.1'), gasPrice: new BigNumber('21000') } }
  />
{/* ) : null} */}

review-fix: Hide vertical overflow on body element so scrollbar not flicker on/off when TxDetails toggled

* Create TxDetails component and move relevant instance methods from TxForm into TxDetails

* Fix linting warning `Using target="_blank" without rel="noopener noreferrer" is a security risk: see https://mathiasbynens.github.io/rel-noopener`