Basic authorization implementation.

	- login and save access token
	- logout and delete access token (only locally)
Help screen updated for login/logout.
Merge branch 'login'

Implementation of 'Basic authentication' for github API.
	- users can login and store access token
	- users can logout and remove access token (locally)

TODO:	Each time user relogin new access token is generated and
	the old one remains unused.