front: Created preference for new input plugin (input-android)

input-android will be a very thin input plugin for communications
between the Android Java front-end and the Mupen64Plus native core.
It will be a simple de-evolution of input-sdl, stripping out all code
not required for the Android front-end, removing dependencies on SDL
and other libraries.
input-android: Initial check-in.

Just input-sdl renamed to input-android. As a Mupen core plugins noob,
it's easier for me to start with a working example and tear down,
rather than building the plugin from the ground up.
input-android: Removed code for loading config from Mupen API.

We are managing all input configuration using Android's scaffolding, so
we do not need to interact with Mupen's configuration file API.
input-android: Removed more stuff related to unused Mupen config API.
input-android: Tell core that all controllers are plugged.

This is just a temporary solution until the actual plugged settings can
be obtained from the front-end.  (Will require an additional JNI func.)
input-android: Removed SDL dependency completely.

This is a bare-minimum removal. A ton of unused code remains, which can
be cleaned up later.

For now, I had to break vibration and in-game pak switching, but for
the most part the plugin is completely functional as far as I can tell.
Anyhow, this is a good base to streamline from.
input-android: Removed unreachable code.
input-android: Removed unreachable __linux__ code.
input-android: Replace printf with generalized debugger calls.
input-android: Formatted code, with no other changes.
input-android: Removed #ifdef _DEBUG directives (redundant?).
input-android: Removed unused #includes.
input-android: Remove more unused code.
input-android: Consolidate some code.
input-android: More streamlining.
input-android: Code rearranged with few other changes.
input-android: Fixed debug logging and cleaned up variable names.
input-android: Remove raw data processing, and more streamlining.
input-android: Eliminated header files, removed unused function.
input-android: Deleted irrelevant doc files.