Add the ability to manage Kapacitor TICKscript template tasks in Chronograf

https://docs.influxdata.com/kapacitor/v1.4/working/template_tasks/#main-nav

A few requirements from a customer:
- [ ] show the variables along with the templates in chronograf
- [ ] ability to edit the values of the variables in chronograf
- [ ] would be awesome to have, an ability to select a template and input various variables for it

Start with the linked Kapacitor template-task documentation and review Chronograf's current task-management behavior. Define how templates and variables should be displayed, edited, and instantiated with user-provided values; done means all three customer requirements are supported and verified in the relevant Chronograf flows.

Written by the indexing model from the issue text.