Add the ability to generate test targets

[JesseTatasciore]

When there are test files present, it would be useful to generate the targets necessary to run those tests

[mattem]

Does the functionality exist in our previous version of gen internally? I think it generated the ts_web_test and ng_web_test macros.

Do we still want that here or should it gen a ts_library and thekarma_web_test_suite?

[JesseTatasciore]

Yes our previous internal version generated for the macros. I would be inclined to say macro. Allows for mass customization of targets / what if someone wants an additional target for whatever reason. Leaves the implementation out of our hands

[mattem]

Seems reasonable, we should look to add ng_web_test and ts_web_test to the index.bzl here. I quite like those as macros anyway.

[Toxicable]

So for our repository we use jasmine_node_test for all our unit testing, this includes both nodejs and browser targets.

Might be worth making it configurable?