Using streamlined parity-ui repository

[tomusdrw]

1. All UI code (Rust + JS) is now in single repository: https://github.com/ethcore/parity-ui
2. Building Parity now requires Node.js.

If everything will go well with this approach, we may merge parity-ui repo to main repo in the (near) future.

[gavofyork]

Windows failing?

     Running `C:\projects\parity-g802m\target\release\build\parity-dapps-status-c341dadc6fc516d8\build-script-build`
error: failed to run custom build command for `parity-dapps-status v0.5.1 (https://github.com/ethcore/parity-ui.git#b0c1fa6c)`
Process didn't exit successfully: `C:\projects\parity-g802m\target\release\build\parity-dapps-status-c341dadc6fc516d8\build-script-build` (exit code: 101)
--- stderr
thread '<main>' panicked at 'Error: Installing dependencies: Error { repr: Os { code: 2, message: "The system cannot find the file specified." } }', C:\projects\parity-g802m\target\release\build\parity-dapps-4797a3edb18c7ec7\out/lib.rs:450
note: Run with `RUST_BACKTRACE=1` for a backtrace

[tomusdrw]

Fixed