Prepare for the android UI module

* Not all pthreads features are supported on Android, thus the changes.
* Changing the `data_store` signature is enough to support nulls because the APIs of both underlying implementations already supported them.
* Declaring the lines for <activity> in the modules allows for non-fullscreen and non-orientation-locked apps!
Hum... Bonne question, la commande de cancellation est dans le passée, mais elle sera appliquée lors de cet appel. Ils utilisent une forme semblable dans le man: _If the calling thread is canceled as a consequence of a call to this function, then the function does not return._