Remove dead initializations
Add %(remote) and %(tag) variables

They complement the %(branch) variable and the former allows
user-defined commands that manipulate remotes as requested by some
users.
Fix refreshing of the stage view after updates

This fixes a regression introduced in the refactoring to support staging
from the main view.
Update tigrc(5) to reflect new view header color
Allow tigrc commands to span multiple lines

Lines ending with a backslash will be continued on the next line.
Move git color mappings to tigrc