@gvaish Don't recreate an activity it it's last on stack

* Controller: if size==1, don't go back.
@gvaish "resetStack" must be made use of post-reponse

* Controller: Reset-Stack after valid response is received
* BaseActivity: Added doNativeBack, onBackPressed can be controlled by the sub-class
* LoginActivity: Reset stack, if successful
* HomeActivity: Exits from the application if user preses back-button twice (within 500ms)