Normalize all asynchronous methods in one

[Reco1I]

In this PR I replace all SyncTaskManager.class and Async.class usages to use Execution alternatives with Kotlin coroutines for asynchronous tasks. That is the composition of the replacements wil be this:

• SyncTaskManager.run() -> Execution.updateThread()

• MainActivity.runOnUpdateThread() -> Execution.updateThread()

• MainActivity.runOnUiThread() -> Execution.mainThread()

Note: Any task that should be done in update thread it's preferable to use Scene.postRunnable() whenever it's posible..

In Kotlin they can be accessed without class qualifier:

• mainThread { }
• updateThread { }