Move Dapps files from @parity/shared ; display icons of builtin dapps from filesystem (#114)

* Remove 'views' dapps

* Remove superfluous variable declaration

* Update @parity/shared dependency

* Move Dapps files from @parity/shared

* Update DappsStore tests (defaultDapps)

They were previously outdated in @parity/shared.

Removed the test "saved views keeps non-specified disabled keys"
because we don't have any dapp to test against in dappsBuiltin.json
(no builtin dapp with a defined id and with visible set to false)

* Fetch icons of builtin dapps from filesystem using manifest.json

* Use require instead of window.require in tests

* Add test for built-in dapps

* Use absolute paths for dapp icons

* Update `@parity/ui` dependency

* Update `dapp-dapp-methods` & `dapp-dapp-visible` dependencies

Had to specify the exact rev in package.json because npm somehow
couldn't properly update the dependencies otherwise:
dapp-dapp-methods would overwrite dapp-dapp-visible in package-lock
and vice versa.

* Factorize getBuildPath() into util/host.js