UI improvements

* Add option to add multiple plugins
* Improve UI hints for collapsed parameters
* Refactored plugins without requirements
* Hide evaluation tab for the moment. You can see it by adding "?evaluation" to
  the URL.

example-plugins/configurable_plugin.py

@@ -43,7 +43,6 @@ class Dictionary(plugins.SentimentPlugin):
 
 class EmojiOnly(Dictionary):
     '''Sentiment annotation with a basic lexicon of emojis'''
-    description = 'A plugin'
     dictionaries = [basic.emojis]
 
     test_cases = [{