[FEATURE] RT-2463 Balances sidebar widget LESS

Add LESS file for displaying account balances in a sidebar widget.
[FEATURE] RT-2463 LESS: Generalize currency colors

Colorization by currency is no longer used by Balance tab only, but also
by Balances sidebar widget.
[FEATURE] RT-2463 Sidebar: Add Balances widget

Add Jade template for sidebar balances widget.
[FEATURE] RT-2463 Balances wid.: Template includes

Include sidebar with balances widget in Send, Trade, Convert tabs.
[FIX] RT-2463 Remove sidebar widgets horizontal padding
Merge pull request #1694 from jublonet/feature/2463-balances-in-sidebar

Add balances widget in sidebar