Update software through Git

... plus a couple of more changes:
1. Update the `git` package bundled into KA Lite.
2. Add settings for setting the default branch and remote to track when git-updating
3. #1926: refresh the page properly when your computer doesn't have an SSD ;)

Also solves #1978.


![image](https://cloud.githubusercontent.com/assets/191955/2736583/6da99b1e-c66f-11e3-8bc1-bfb550689beb.png)