PluginGenerator: added possibilities to generate plugin of given type.

* Added possibility to select and generate the plugins of appropriate
  available types (Processor, RecordEngine, DataThread, FileSource).
  Now it's only generates appropriate lib files and selects some types
  in processor. However, we should generate different processor files
  for each plugin type later.
* Added possibility to select processor type;
* Some refactoring of existing code and minor fixes;
* Still needs some refactoring of newer code with some improvements.