Log Message:
Update mikutter to 3.1.

Features
* drop Ruby 1.9 support.
* activity
  * blushup activity setting UI
* extract
  * scrollable with many data sources
  * hierachized data source
* list
  * obsolate list tab, list data source is provided instead.
* openimg
  * support multi image attachment tweet
* profile
  * scrollable with may belong list tab
* uitranslate
  * new language, Kansai accent
API
  * Add `defined_time' Plugin DSL method to retrieve plugin loaded time
  * obsolate MessageConverter, add functional to rewrite Message for Entity