Edit on GitHub extension for sphinx
Fix edit_on_github extension
Move _ext and _templates to common/
Add .gitignore to ext/
Add option to specify edit_on_github_prefix value

Fix omero/conf.py to use 'omero' as the prefix
Fix Edit on GitHub branch and prefixes
Update index.txt

Add sentence about the new "Edit on GitHub" button
as a test of the new "Edit on GitHub" button.

Cheers,
~@joshmoore
Add missing prefixes
Merge pull request #801 from sbesson/rebased/develop/edit-button

Add Edit on Github button (rebased onto develop)
Merge pull request #802 from snoopycrimecop/patch-1

Update index.txt