pants: Deprecate the `dependencies` alias in favor of `target`

Deprecate the `dependencies` alias in favor of `target`, as discussed at https://groups.google.com/d/topic/pants-devel/F9eRdBXB8Lo/discussion

Testing Done:
Replaced all instances of 'dependencies' in pants own BUILD files, but not in tests.

Passes ci.sh.

Outputs the following warning:
WARNING:root:For src/java/com/pants/testproject/proto-ordering:proto-ordering : The alias 'dependencies(..)' has been deprecated in favor of 'target(..)'

Reviewed at https://rbcommons.com/s/twitter/r/899/