fix some display issues
Added proper template inheritance
Basic frontend support for Persona
change top bar
Use spaces for indentation (grumble grumble…)
Reformat source files to under 80 chars
Multiuser placeholder
Add failing test for merges where only different files change
Tidy up WikiPage.save
Refactor tree-walking logic to allow for automatic merging
Don't throw away changes when multiple files are being edited at the same time.

Instead, if the only changes are to other files, merge; if there are changes to
the file we're working on or the commit an edit was based on has been rebased,
we just throw an exception for now.