bumped the version to 1.7
updated changelog and contributing instructions
update submodule references
Merge branch '1.8/develop' of https://github.com/fuel/fuel into 1.7/master
updated the changelog
Added missing v1.6.1. section. Related https://github.com/fuel/fuel/commit/1c4e81b3941c833a8dcf0e6565d4bbe68dc65f03
Merge git://github.com/fuel/fuel into 1.8/develop

Conflicts:
	docs
	fuel/core
	fuel/packages/orm