* Allow topBar.title.color reset when color isn't provided

* Reset to nil color

* Merge topBar options with default

* Fix topBar options merging

Co-authored-by: Guy Carmeli <guyca@users.noreply.github.com>

Fix TopBar title animation. This commit changes how RNN handles title and subtitle.
Until now, RNN created a custom view for title and subtitle which interfered with the way the system animated the TopBar title.
With this commit the custom view is created only when both subtitle and title are declared, otherwise RNN uses the system behavior.