deprecated reflect mode has been replaced with import mode

[tulzke]

resolves https://github.com/uber-go/mock/issues/175 resolves https://github.com/uber-go/mock/issues/197 resolves https://github.com/uber-go/mock/issues/128

It is impossible to create an mock for a generic interface via reflect mode, because it is impossible to compile a generic type without instantiation. This PR replaces the reflect mod for parsing using go/types.

All exists mocks have been regenerated and the tests have been passed. But since this radically changes the behavior of reflect mode, I would be grateful if there are those who want to add additional test cases that I did not provide.

We can also come up with another name instead of import mode.

benefits:

• generation mocks for generic interfaces
• generation mocks for aliases to interfaces
• correct names for method arguments