Add a console section to the settings page

[Roasbeef]

A "console" page should be added to the settings page. This would let users manually enter lncli commands like adding peers, listing their channels, changing the debuglevel, etc.

Such a page would also aide in debugging as users will be able to input directed commands in order to get a better feel for what the issue at hand is.

[tanx]

Duplicate of #414