Fix a few hitches in the install process

* Use https instead of ssh for .emacs.d submodule
* Change -f to -y when removing unity webapp stuff
* Remove accidental extra protocol from readme install instructions
Set git to use sensible-editor, so it uses preferred editor.
Use environment variable over .gitconfig, which should be more resilient.
Fix .xsessionrc so it won't fail.

* .xsessionrc will run a bash shell directly because it's not executed by bash
Install script will fix up push location in homedir too.