Fix Instagram content type id (18 -> 19)

Instagram content will actually have a type indexed with “19” not “18”.

Also use a macro to check for bounds before applying content source map.

Standardize naming: LFSContentInstagram -> LFSContentSourceInstagram
Merge pull request #23 from Livefyre/rc2

Standardize naming: LFSContentInstagram -> LFSContentSourceInstagram