Use segment `branch` for all VCSs including perforce.

Use the same segment `branch` to first check if the environment has the
BRANCHNAME variable set (for perforce), if not check for other VCSs.
Use bold attribute for displaying branch info.

In the termsaber tmux theme, use bold attribute for displaying the
info in the branch segment.
Fixed error in parsing termsaber tmux theme config.
Clenup unused segments from tmux termsaber theme/colorscheme.
Fix typo that caused error in parsing config file.

Fix the typo that caused an error in parsing the termsaber shell theme.
Fix failing tests in default coloscheme for tmux.

Add the additional segments from termsaber into default coloscheme for
tmux, without which the tests fail.