Build options and tags for modules

[JoTurk]

During the discussion there was suggestions about doing transcending, support sqlite and many other options.
I think by default ION should only build and link to pure go libraries, and we can provide a tag enable_cgo which by default enables modules like sqlite (enable_sqlite | disable_sqlite), for builtin transcoding in the future we can add tags for building with ffmpeg.
This should provide the ability to build a small and minimal version of the sfu.
This is deeply tied to how we'll do the DI and configs.

tasks:

• provide a system to automatically log if a module is missing from the build if a user tried to configure it.
• Define a naming convention, I think we should use both enable_ and disable_