Added the UpdateDefaultTheme function.
Renamed panelRenderTemplate to renderTemplate.
Renamed panelSuccessRedirect to successRedirect.
Reduced the amount of boilerplate in panel.GroupsEdit with renderTemplate.
Renamed the pre_render_panel_edit_group hook to pre_render_panel_group_edit.
Reduced the amount of boilerplate in panel.GroupsEditPerms with renderTemplate.
Renamed the pre_render_panel_edit_group_perms hook to pre_render_panel_group_edit_perms.
Fixed a bug where the active status for themes didn't get loaded at start-up.
Fixed a theoretical deadlock in NewThemeList.
Updated CONTRIBUTING.md
Fixed the punctuation on a couple of registration errors, these will be localised too soon enough.
Removed a bit of boiletplate in groups.go with buildBasePage.
