Non-member function organization for hhbc-translator

Summary: Replace hhbc translator with a state structure and non-member
functions.  The "public" functions are in irgen.h right now, but the API feels
like we have the wrong abstraction boundary to me (things like
"incTransCounter" are pretty odd functions to have---my thought is
translateRegion and selectTracelet should probably be the only two "public"
functions to the IR frontend eventually.)  I don't think this is an ideal final
state still, basically...

Reviewed By: @swtaarrs

Differential Revision: D1708554
Do a few small TODOs left out of D1708554

Summary: Except the minstr makeCatch thing, which might require some thinking.

Reviewed By: @alexmalyshev

Differential Revision: D1708575