Make the scheduler frequency tunable via ENV.
Fix a bug where the `disable` action did not work in SchedulerAgent.

Bad specs are fixed and specs that should be common among agents that
include AgentControllerConcern have been extracted to
spec/support/shared_examples/agent_controller_concern.rb.
Make `action` a mandatory option in preparation for making it interpolated.
Make `action` interpolated.
Merge branch 'fix-scheduler_agent'
Add CommanderAgent, which controls other agents on a schedule or incoming event.
Get the new Dropbox Watch Agent off the ground.
Send events when the Dropbox Watch Agent detects any difference on the directory listing provided by the Dropbox API.
Implement dropbox directory diff. Very naive.
Merge pull request #569 from knu/scheduler_frequency

Make the scheduler frequency tunable via ENV.
Merge pull request #570 from knu/commander_agent

Add CommanderAgent, which controls other agents on a schedule or incoming event.
Disable CSRF token verification in WebRequestsController.

This should suppress the "Can't verify CSRF token authenticity" warning.
`before_filter` is called `before_action` in Rails 4+.
Merge pull request #571 from knu/disable_csrf_warning

Disable the CSRF warning in WebRequestsController
Make action icons look clickable.
Rename icon_for_service() to omniauth_provider_icon().
Add omniauth_provider_name().
Use yes_no().
Add omniauth_button() and use some Sass tricks for DRY.
Alter the caption text format for services.

"(Twitter) knu" -> "Twitter: knu"