[Help] Add a line break to GPIO help
[License] Add license file indicating fppconvert is GPL v3

The rest of FPP is GPL v2, but fppconvert uses xLights source code
so that makes fppconvert GPL v3.
[License] Add a license file for external components and their URLs
[Testing] Add a Channel and Sequence test screen to the UI.
[Debugging] Update debug log to show proper channel numbers
[Media] Add mediaOffset setting to allow adjusting sync offset
[Media] Add oggPlayer and mp3Player hidden settings

These allow overriding the use of /usr/bin/mpg123 and /usr/bin/ogg123
directly to allow testing outputs other than ALSA.