pidgin.h phase3: create pidgin.h and force its usage

fix the section id of pidgincore.h

Generate our pidgin.h file

Add include guard to all pidgin/*.h files and deal with the fallout from that.

Also had to namespace PIDGIN_BLIST_COLUMN_NAME, will come back and get the rest at a later time.

Testing Done:
Compile test, including some plugins that don't build by default. Also ran everything seems fine.

Reviewed at https://reviews.imfreedom.org/r/50/