finished mocked create renderer impl and first test cases

[robpatriot]

A few thoughts here:

1. I used mocks for the dir for the fake vertex only impl of createmeshrenderer and put them in the mocks package. Maybe we want to keep these separate from actual gomock mocks? Either gologo_mocks or maybe some other non mocks based naming
2. The opengl mocks file is called that because it uses the concrete definition of MeshRenderer. It also needs to return a MeshRenderer to pass to InitFromRenderer. Therefore I think this is reasonable but then I guess it breaks our idea of mocks because it depends on the very thing it's trying to "mock"

[leedenison]

I think this is fine. But maybe call it a fake rather than a mock?