Adding Sound output plugin

[theZiz]

This pull request adds a new plugin (https://pyra-handheld.com/boards/threads/sound-output-plugin-for-pandora-configbutton.79781/) for KickAss' pas.sh script for the easy use of bluetooth headsets over alsa (https://pyra-handheld.com/boards/threads/pandora-audio-switch.77143/).

It is tested by three persons and did not show any bugs (anymore).

Furthermore the PR improves the Makefile of the plugins, so that they can be installed if compiled on the pandora, and that you can compile just one plugin instead of all and that you can compile in parallel. It also makes the Makefile shorter and a new plugin does not need to edit the Makefile add all as just all C files in the plugin folder are compiled.

[slaeshjag]

Look alright. A few minor things:
Indentation is all over the place in configbutton.h, it should be consistent file-wide
Embedding the zip as base64 seems very silly, you could just link it in as a hunk of binary data. See http://stackoverflow.com/questions/4864866/c-c-with-gcc-statically-add-resource-files-to-executable-library/11622727#11622727

[theZiz]

Sounds interesting, I will have a look at it. Although I like the file inside a header approach :)