Several fixes

* Refactored BaseModel for efficiency
* Added plugin metaclass to keep track of plugin types
* Moved plugins to examples dir (in a previous commit)
* Simplified validation in parse_params
* Added convenience methods to mock requests in tests
* Changed help schema to use `.valid_parameters` instead of `.parameters`,
which was used in results to show parameters provided by the user.
* Improved UI
    * Added basic parameters
    * Fixed bugs in parameter handling
    * Refactored and cleaned code

senpy/__main__.py

@@ -67,7 +67,7 @@ def main():
         '--plugins-folder',
         '-f',
         type=str,
-        default='plugins',
+        default='.',
         help='Where to look for plugins.')
     parser.add_argument(
         '--only-install',