Updated tmux config to remove C-a last pane bind

The C-a last pane bind was redundant; the ; (semicolon) bind does the
same thing.
Modified git log/graph output color schemes
Added git alias 'noff' to force no fast-forwarding
Refactored install script

Refactored install script to make it cleaner and make it compatible with
both Python 2 and Python 3.
Updated git diff aliases

Updated aliases to not use the '--color-words' option by default because
it can make it hard to read certain outputs.
Updated iterm2 color scheme

Fixed black background color.
Added minimal zsh prompt