The user has the option to go to 'Shortcuts' -> 'Search engine settings' to
modify the default search engine. When returning from that settings screen we
need to update it to account for any changes.
For this we will check the current default engine against a previously stored
value in a newly added 'defaultEngineSource' property from SearchState class.
Also, I modified 'SearchStoreTest' by adding the new parameter to the
'SearchState' constructor.
* For #3633 - Adds SearchStore
* For #3633 - Refactors AwesomeBarUIView
* For #3633 - Refactors ToolbarUIView to use lib-state
* For #3633 - Fixes a couple of state bugs
* For #3633 - Moves all user interaction to SearchInteractor
* For #3633 - Adds kdocs to SearchStore and SearchInteractor
* For #3633 - Adds documentation for the properties on SearchState
Also removes uneccessary property
* For #3633 - Creates `StateViewModel` to handle state restoration
* For #3633 - Adds a test for onTextChanged
* For #3633 - Adds tests for SearchInteractor
* For #3633 - Fixes bugs and adds documentation
Simon Chae