Add template supergrouping.

This allows adding a "super template group" to an existing template. This is most of the meat from the
pull request at https://github.com/brianm/jdbi/pull/87 from @sbrossie.
Add StringTemplate3StatementLocator builder.

Assuming, that any class with seven different constructors is bad
anyway, deprecate all of them except the all-args constructor, make
that private and add a builder to create an instance.
Parallelize the tests.

Shaves about a minute off the build.