[Tests] Test app going on background and foreground

Signed-off-by: Miguel M. Almeida <miguelcma@gmail.com>
[Reset] softReset missing [Liquid destroySingleton]

Signed-off-by: Miguel M. Almeida <miguelcma@gmail.com>
[Fix] concurrency issues + Invalidation is now immediate

* Fixed a lot of concurrency issues that could happen in edge situation
* Invalidation of a target is now done on the main thread (synced and not asynced),
which means it will be immediatelly invalidated for the very next variable that is used.

Signed-off-by: Miguel M. Almeida <miguelcma@gmail.com>