automatically add import for types when applying content-assist proposals for query methods

[martinlippert]

I invoke content-assist within a Spring Data repository interface and select the one that generates the full method signature, e.g.:

List<Customer> findByFirstName(String firstName);

But there is no import statement added for the java.util.List type in this case. The content-assist should add that necessary import automatically if the import is not yet there.

[BoykoAlex]

Should be fixed with e273a94