Alyssa/add wire support

I think there are a lot of these we don't need.  They correspond to the imports lines in the wire_gen.py python file.  It can be hard to get them exactly right.  Once you get a `test_wire_gen.py` test going, you can comment out ones you think aren't needed, then run the test and see if all of your imports can be found.  When you write the test, invoke it as follows:

```
./pants goal test tests/python/pants_test/backend/codegen/tasks:wire_gen
```