GPII-345: Adding a new and functional GPII Activity

This commit brings a new UI for the Android's GPII application activity.
Within the new design, we're providing some useful features to the user.

  * start/stop/kill the GPII instance of the device through the UI
  * Check the current status of GPII

Do do that, we've made the following changes:

  * Create the layout for the new UI
  * Include the Java code for the new UI
  * Add all the translatable stings into strings.xml
  * Add the logo of the GPII project

In addition to this, reviewers (or anyone who is trying to test this pull request) must know that the "stop" button isn't working as expected due to this bug [https://github.com/paddybyers/anode/issues/25].
The side effects of this bug is that we're not able to ensure if the GPII is running or not after stopping it. That's because the port where the GPII is listening at, isn't released after stopping the GPII, so you have to kill the main process in order to ensure that the GPII is being stopped, and the port is being released well.

Cheers,
Javi