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/schemas/plugin.json

@@ -1,7 +1,7 @@
 {
   "$schema": "http://json-schema.org/draft-04/schema#",
   "type": "object",
-  "required": ["@id", "extra_params"],
+  "required": ["@id", "name", "description", "version", "plugin_type"],
   "properties": {
     "@id": {
       "type": "string",
@@ -9,7 +9,19 @@
     },
     "name": {
       "type": "string",
-      "description": "The name of the plugin, which will be used in the algorithm detection phase"
+      "description": "The name of the plugin, which will be used in the algorithm detection phase."
+    },
+    "description": {
+      "type": "string",
+      "description": "A summary of what the plugin does, and pointers to further information."
+    },
+    "version": {
+      "type": "string",
+      "description": "The version of the plugin."
+    },
+    "plugin_type": {
+      "type": "string",
+      "description": "Sub-type of plugin. e.g. sentimentPlugin"
     },
     "extra_params": {
       "type": "object",