v1.2.0: Remote interaction, diffing and more

• Add the mf keymap to run Fugitive's :Gmerge
• Add merginal#branchDetails for better parsing of the branch info
• Add ct and cT for tracking remote branches
• Add ps,pl and pf to push, pull and fetch branches
• Make dd be able to delete remote branches
• bd in the branch list opens the diff files buffer to diff against the
  selected branch.