Merge remote-tracking branch 'origin/dsander-omniauth'

Conflicts:
	Gemfile.lock
Set charset/collation properly for each text column if using MySQL.

With this change, Huginn is able to store up to 4-byte UTF-8 characters
in its database.  This should fix #286.
Add support for Ruby 1.9.x.
Fall back utf8mb4 to utf8 if the server does not support it.
Follow the default collation of Rails rather than MySQL.

`utf8*_unicode_ci` is known to be problematic in some languages like
Japanese, but hopefully it wouldn't do harm in practice in our case.
Merge remote-tracking branch 'origin/master' into set_charset_for_mysql

Conflicts:
	db/schema.rb
Add app.json.
Support installation via Heroku button.
Place a "Deploy to Heroku" button.
Fix app_name.
Update the Heroku instructions.
Merge pull request #414 from knu/set_charset_for_mysql

Set charset/collation properly for each text column if using MySQL.
Merge pull request #464 from knu/heroku_button

Add a "Deploy to Heroku" button.
Cleanup event references on AgentLogs when Events are deleted
allow separate events for each answer in the HumanTaskAgent
Merge pull request #475 from cantino/human_task_agent_separate_events

allow separate events for each answer in the HumanTaskAgent
Merge pull request #473 from cantino/nullify_agent_log_event_refs

Cleanup event references on AgentLogs when Events are deleted
Remove "locals" from Drop classes and introduce a real context class.

The Context class is capable of switching a self object and adding local
variables, and also hashable for the convenience of being used as a
cache key.

As for the thread safety, we give it up for now as we don't support it
or have concurrency tests yet anyway.
WebsiteAgent: Provide a variable _response_ for interpolation.

* `_response_.headers.Header-Name` is expanded to the value of header
  named _Header-Name_.

* `_response_.status` is expanded to the HTTP status as integer, which
  is almost always 200, since currently the WebsiteAgent will only
  create an event when a request succeeds, and the request method is
  limited to GET.