Allow utf-8 bucket types

Can now create, enable, etc unicode bucket type names. Have verified that adding and retrieving keys work correctly via both HTTP and PB, but other than that and the tests added to `riak_test` (below) this has not been extensively tested.

Corresponding `riak_test` PR: basho/riak_test#549

/cc @jrwest 

(Replaces #866, which included unnecessary whitespace removals)