Allow widgets to have a custom state and action when tapped

**Is your feature request related to a problem? Please describe.**
I want to show the state of a sensor as a widget, and trigger events when clicking that sensor. This is currently not possible AFAIK.

**Describe the solution you'd like**
- Allow the Entity State widget to have templating for the main text of the widget (not the small label)
- Allow the Template widget to trigger actions
- Allow sensor sensors to register actions

**Describe alternatives you've considered, if any**

**Additional context**