rebase merge with conflicts

Added

• support rebasing branches with conflicts (#895)
• add a key binding to stage / unstage items [@alessandroasm] (#909)
• switch to status tab after merging or rebasing with conflicts (#926)

Fixed

• fix supported checkout of hierarchical branchnames (#921)
• appropriate error message when pulling deleted remote branch (#911)
• improved color contrast in branches popup for light themes [@Cottser] (#922)
• use git_message_prettify for commit messages (#917)

Support