Update iTerm2 settings

Change-Id: I1d9c8663bd797637613c55cfb87fe80d5543ffcf
Add difftool and mergetool settings to .gitconfig

Change-Id: I91f1b990c88ada6a03d3e34e2db44d87f459f17f
Add global gitignore

Change-Id: I87f78061791ae26f57d072ba4ad6cbcc91232a25