Factor out the dimensions detection login into a DimensionsDetector component.

If the view gets resized to a 1:1 aspect ratio, remember the previous mode to
avoid flickering when going back to a larger size or different aspect ratio.

Adds the ability to detect app area's aspect ratio on react-native
through the features/base/aspect-ratio.

Makes conference, filmstrip and toolbox react to the aspect ratio
changes and display filmstrip on the shorter side of the screen.