Implemented a scalable control pad

[poisdeux]

This should hopefully fix issue #383 and fix the issue with the original version from PR #428. The original version did not include a check to see if the event server was disabled by the user. This was probably the reason some users reported issues with the control pad not working during the beta release of 2.3.X.

I falsely assumed that checking if the event server connection failed, the variable eventServerConnection would be set to null. This is only the case if hostname resolving fails. Thus, if the event server is not available and the user disabled its usage we would still be using it and do not fall back to using the HTTP input events. This has been fixed now.

In general the following changes have been made in this PR:

• Refactored RemoteFragment and created a compound view for the
  actual remote. I called it ControlPad to make it more clear what
  its main function is.
• Implemented a custom grid layout (SquareGridLayout) that will
  always be square. When its width and height are both set to
  match_parent, it will take the smallest of the two as the
  actual size.
• For devices with a smallest width smaller then 360dp the ControlPad
  is sized to the maximum available space. For larger devices we still
  use the old fixed sizes.

[SyncedSynapse]

Looks good at first sight. Let me just test a little bit more.

[SyncedSynapse]

@poisdeux Just one observation: With this PR we get 2 fragment_remote that look very similar (both in portrait and in landscape). The only differences that i could see (in the portrait version) are the FrameLayout that surrounds the top panel on the non-360dp version (which i didn't really understood why it was needed, can't it be removed?) and the FrameLayout that surrounds the control pad on the 360dp version.

Can't this be done using the same fragment_remote, applying different styles? I mean, keep the necessary FrameLayouts and give them a style that gets set to wrap_content or a fixed dimension depending on the version.

[poisdeux]

Good suggestion. I changed the code to use two new styles for devices with a smallest width equal or bigger then 360dp. One for portrait orientation and one for landscape orientation. That should reduce the duplication considerably.