Add a blank models.py to reviewboard/webapi/.
Add a blank models.py to reviewboard/webapi/.

This will help with import errors when switching back-and-forth between
release-2.0.x and master.

beol/reviewboard,bkochendorfer/reviewboard,davidt/reviewboard,KnowNo/reviewboard,beol/reviewboard,brennie/reviewboard,sgallagher/reviewboard,bkochendorfer/reviewboard,KnowNo/reviewboard,sgallagher/reviewboard,custode/reviewboard,brennie/reviewboard,reviewboard/reviewboard,reviewboard/reviewboard,sgallagher/reviewboard,KnowNo/reviewboard,davidt/reviewboard,custode/reviewboard,brennie/reviewboard,bkochendorfer/reviewboard,custode/reviewboard,reviewboard/reviewboard,KnowNo/reviewboard,chipx86/reviewboard,brennie/reviewboard,reviewboard/reviewboard,chipx86/reviewboard,bkochendorfer/reviewboard,beol/reviewboard,chipx86/reviewboard,custode/reviewboard,chipx86/reviewboard,davidt/reviewboard,davidt/reviewboard,beol/reviewboard,sgallagher/reviewboard