TrustedCredentials: Don't crash when the activity is paused

If you press Settings -> Security -> Trusted Credentials, then press
 back before the loading finishes, the loader async task will still
try to dereference the activity which will cause an NPE.

This patch fixes that by getting and holding a reference to the
context in the beggining and bailing early if it is null.

Change-Id: Ie03734d5f184821df5d8729fc4a16eb51cdeebf5
Answer call with hardware HOME button (1/2)

Squashed commit of the following:

Author: Oleksandr Byelkin <sanja.byelkin@gmail.com>
Adds ability to answer call with hardware HOME button
preparation to winter time
Change-Id: I0d22a6fbb92a61f08b50cae5c14d0030b81ee6ec

Author: Michael Bestas <mikeioannina@gmail.com>
Settings: Move home answer & power end call options

Move 'Home answers call' & 'Power ends call' options to button settings
Change-Id: I2f365a3d278b0845b7c5ffcfe70c54160a00c24e