tim-connector: Changes in JobSchedulerController and zul

Lots of changes:
* Created a new model to follow the standard structure of controllers in
  LibrePlan.
* Marked several strings to be internationalized.
* Improved .zul page, removing unneeded stuff and simplifying code.
* Checked that cron expression is right, otherwise inform the user.

FEA: ItEr77S16JiraAndTimConnectorContributionIntegration