perf($q): move Deferred and Promise methods to prototypes

Opening PR for tests and comparison with other solutions for `$q` perf.

NOTE: Deferred doesn't get all the advantages of moving methods to the prototype,
since the constructor binds instance methods to "this" to support unbounded execution.

NOTE: This change increases the gzipped version by 100 bytes.
I agree it would make sense to consolidate the two constructors, but I'd like to keep this PR as a simple refactor. To consolidate them would require changing semantics of Deferred.