.config/xfce4/help.rc: Ignore help key.

Annoying when a console program (e.g., htop) uses F1 and the terminal
emulator insists on popping up a web browser for "help".
.vimrc: Only set GUI font if actually in GUI.
.vimrc: Set more options.
Powerline shell prompts.
.vimrc: Replace sucky Molokai airline colours with Airlineish.
.vimrc: Fix and enable tabline.
.vimrc: Enable whitespace checks.

Particularly important for Python (mixed indent, or PEP 8 against
trailing whitespace), and keeping diffs clean (git flagging trailing
whitespace).
.config/xfce4/terminal/terminalrc: Init preferred options.