Reviewed InputFilter input filter

- Refactored tests to match those of RPC/REST/Documentation
- Refactored input filter to extend InputFilter (instead of implement
  InputFilterInterface), and to accept a Factory instance to the constructor.
- Updated InputFilterInputFilter factory to ensure it's injected
  with a factory instance that's aware of configured filters and validators.
Added ag-form to input filter editing screen

- added <form> tag with ag-form directive to input filter edit screen;
  removed <form> tag from around the "new field" input/button.
- added agFormHandler to input filter controller, and incorporated into
  save logic
- fixed factory for InputFilterInputFilter (was referencing invalid
  class name when instantiating filter)