adding Organization#submissions([query], callback) + tests
Merge branch 'feature/organization-submissions' into dev

Conflicts:
	lib/graph/Organization.js
	test/lib/graph/Organization.js
version bump + changelog update
removing debug usage from lib (never used it)
Merge branch 'release/0.5.1'
Merge tag 'v0.5.1' into dev

v0.5.1 release
 * Removing `debug` usage from lib (never used it)
 * Updating documentation
 * Adding `Organization#submissions()`