[addonmanager] refactor GetAllAddons

- change to not return duplicate addons (one for every extension point)
- remove the allowRepos parameter
- move old GetAllAddons to json rpc to keep backward compatibility
[addonbrowser] replace enabled/disabled with user installed/system category
[addonbrowser] orphaned wip
[addonbrowser] hide add-on categories user shouldn't install from
[addonbrowser] don't display repos as folders in 'all'. we already selected repo
[addonbrowser] rearrange root menu
[addonbrowser] remove date sorting. doesn't work