Fix: indexer exposes IEnumerable.

Fix: Expose indexer on RegionManager.

Fix: clear items from region.

Feat: RegionItemsControl

Feat: add RegionItemsControl

Fix: add dependency Microsoft.Extensions.DependencyInjection

Merge remote-tracking branch 'origin/master'

Fix: return if region exists.

Fix broken links in index.md

Fix docfx not rendering table properly.

Update docs.

Add WIP notice to index.md.

Add docs for DialogService.

Merge remote-tracking branch 'origin/master'

Match interface nullability.