Update to ItemGrid (Movies)

[neilsb]

Update to styling and behaviour of Item Grid (for Movies):

Changes

• Added base JFContent to extend current Data Items
• Load grid items in background task (Fixes Load Content Asynchronously #220)
• Continuous Scroll (Fixes Continuous Library Scroll #219)
• Improve spacing and item highlighting - Focused item now zoomed and Movie Title only shown when focused (Fixes Suggestion for better readibility #202)
• Ensure content in Safe Zones (Refs Modify GUI to support roku safe zones #182)
• Show backdrop of focused item (Fixes Show Transparent Image of Focused Media #6 )

Idea behind 'JFContent' item is that it will have a common set of properties across all content types, allowing other reusable Components to display any content item without worrying about type. (Can replace HomeItem later)

This adds a new ItemGrid2 component and is used to Display Movies. Can replace existing ItemGrid and allow displaying of other content (TV Series, Photos, Music Albums, etc)

Only Movies were edited to try and keep size of PR small to air review. Enabling for other content types should be straightforward.

[anthonylavado]

Looks good to me on my device!

One concern which we can address later if you wish, which is that if an item doesn't have a backdrop, it stays on the previously shown backdrop. I don't know if we want to keep that or change to a default background instead.

[neilsb]

if an item doesn't have a backdrop, it stays on the previously shown backdrop. I don't know if we want to keep that or change to a default background instead.

Yeah, I wasn't sure. It was a conscious decision to leave it on the last shown one, rather than have it revert to a black background, but I'm happy for it to work either way.

And when we get the user settings screen sorted there will be an option to disable the backdrops while browsing.

[anthonylavado]

I'm okay with leaving it on the last shown one. Most things should have backdrops, and I think the black would be too jarring.