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

example-plugins/async_plugin/asyncplugin.py

@@ -0,0 +1,26 @@
+from senpy.plugins import AnalysisPlugin
+
+import multiprocessing
+
+
+def _train(process_number):
+    return process_number
+
+
+class AsyncPlugin(AnalysisPlugin):
+    def _do_async(self, num_processes):
+        pool = multiprocessing.Pool(processes=num_processes)
+        values = pool.map(_train, range(num_processes))
+
+        return values
+
+    def activate(self):
+        self.value = self._do_async(4)
+
+    def analyse_entry(self, entry, params):
+        values = self._do_async(2)
+        entry.async_values = values
+        yield entry
+
+    def test(self):
+        pass

example-plugins/async_plugin/asyncplugin.senpy

@@ -0,0 +1,8 @@
+---
+name: Async
+module: asyncplugin
+description: I am async
+author: "@balkian"
+version: '0.1'
+async: true
+extra_params: {}