React 16 (#7174)

* Update packages to use React 16

* Rollback to react-router v3

* Use component instead of pure one

* Remove warning about mobx

* Make webpack load css from @parity/ui

* Update enzyme to support react16

* Fix lint

* Use @parity/ui v3

* Update refs of plugin-signer-* deps

* Exclude plugin-signer-* from babel processing

* Reupdate refs to old method

* Update refs again