Generate tests for methods from nested/inner classes in plugin

[volivan239]

Description

Currently, the engine and codegen are able to generate tests for methods that are in nested/inner classes (such tests are generated in contest estimator, for example). But plugin does not support this.

Expected behavior

Launch plugin on the class A from the following example:

class A {
    static public class B {
        int sum(int a, int b) {
            return a + b;
        }
    }
}

Expected behavior is that a dialog proposing to generate tests for A$B.f() is shown in UI and some tests are generated after pressing OK. Also, if you create tests for package containing this class, tests for this method are generated.