Adding repo menu item
Display the repos dialog from the menu item
Populate table data
Add sorting to the repos dialog

Extracted a HasSortableWidget class so that sorting can be
attached to any widget that has sortable columns
Fixup enabled/disable overrides.
Fixing repo_lib call after rebase
Show error on enabled override update exception
Do not apply overrides when fetching repos from certificates
Properly update cache when overrides are modified

When we modify the overrides on the server, the current
set of overrides are returned, so there is no need to have
the cache fetch them again when it is updated.

Added an update_local method to the cache so that the current
cache could be reset to the specified overrides.
No need to build a dict of the repos
Use the correct parent when showing error/confirm dialogs.
Disable reset button and fix sorting issue
Disable Repositories menu item when not registered
Fix error on initial sort by 'modified' column.
No longer retrieve overrides twice per update.
Fixing glade files
Removed unused glade file
Moved Repositories menu above Preferences
Bold the repo id when confirming reset.
Make compatible with RHEL6 gtk version.