Updates: user interface changes

[antonlacon]

This builds on #301. Its commits are included here. @flubshi you're the only user I know of who may create their own custom releases.json instead of using custom to fill in the LE testing one if you wish to test this.

This adds a ReleaseChannel toggle that switches the releases.json it uses from looking at releases.libreelec.tv to test.libreelec.tv to a user defined custom URL ("stable", "testing", and "custom" respectively).

This does some menu element hiding/revealing based on which release channel is being used (ex: autoupdates only apply to the stable channel). It also refreshes the releases.json it checks for version and available builds when the release channel changes. This can be a noticeable delay if on slow wifi between changing the release channel and the menu reloading.

Other interface changes are locale updates and deleting the custom channel 2 and 3 (custom channel 1 becomes the value used for the custom release channel).

Autoupdate is disabled (stats shared, but it halts the check after submission) if not on the stable release. Screenshots follow:

Default (stable channel, autoupdates on):

Stable channel, autoupdates off:

Testing channel:

Custom channel (URL would be shown if entered):

Draft until others look at the strings before squashing and 301 goes in.

[chewitt]

I'd ask that Automatic Updates sits underneath Available Versions so there's a logical progression between Channel > Release > Versions .. before we get to the update features that apply them. Otherwise (from a GUI perspective as I should never be allowed to review Python code) .. looks fab :)

[antonlacon]

I tried it and I found having the automatic update toggle expanding options above it, instead of below it, to be odd.

I see the progression as "Will the system manage the updates? y/n" and then giving the user what their choices are when answering n.

[flubshi]

I have used my custom URL when there was no official releases.json for testing. Since there was an official releases.json for testing, I switched to this URL channel.

But it would be nice to keep this feature, in case some "testing forks", like for instance Montellese "Media importing" would like to make use of it.