Minor changes in Git aliases

- change gr to git remote to git rebase. In a daily developement,
  for a typical developper, ther is more rebase than adding or
  removing branches. Thus, gr (for git remote) becomes gre, while
  gr becomes git rebase (gr = rebase, gra = abort rebase,
  grc = rebase continue)
- gf is for git fetch. new alias for --all: gfa
- gmt is nof git merge tool with kdiff3. gmtvim is also defined for
  vim-lovers.
- gitk-entier-history is a useful alias for find lost/dandling
  commits without having to mess with git reflog

Signed-off-by: Gaetan Semet <gaetan@xeberon.net>