Fixed and slightly improved crash detection mechanism.

Before, if a crash was detected, but the "Force quit" dialog remained on the screen, sending the intent to restart the executor would do nothing. It's fixed now with default
uncaught exception handler. Also, when we catch the uncaught exception, we can restart the executor straight away, without waiting for the time-out.

Change-Id: I2f0b4b5f2abd180ff518f1a40ad1294bed2f7f67