[addons] switch general.addonupdates to an integer setting. Skins can use a button control for the setting instead of a
toggle.
[addons] adds 'never' as an option for the addon update setting
[confluence] use a button for the addon update setting to allow for 'never' as an option
[addons] change root of add-on manager to unsorted rather than sort by label
[addons] adds LastRepoUpdate() to the add-on installer
[addons] adds 'Check for updates' to the root of the add-ons manager.
[addons] show all add-ons in the add-on manager, including libraries/modules/helpers
Merge pull request #4287 from jmarshallnz/neverneverland

[addons] add support for 'never' updating or checking for updates