Allow deletion of scheduled jobs from resque web

This is a feature that my team has wanted for a while, so I went ahead and added it.  You can now go to the schedule tab and delete any job as long as you are running in dynamic mode.

The addition of the delete endpoint angered rubocop, so I factored out the helpers and lowered the max length config for methods.  How would you feel about adding a rubocop exception to the ResqueScheduler::Server.included method so that this method doesn't force an artificially high max line length?  It made sense to factor out the helpers, but the routes themselves seem okay as they are.

When I moved the helper methods into the module, rubocop complained that '[]' should be used instead of 'Array.new'.  I'm not sure why that was masked before.