Feature request: Calendar Vertical Indicator without text

[rdewolff]

Describe the feature you'd like
As a user, I'd like to have some particular indicator in the agenda with custom color and size. This could allow to displa availabilites, or other indication that do not contain text but could be clicked.

Visual demo
Here is a visual demo taken from amie.so app. The green bar are what am talking about.

That'd be amazing!

[pdpino]

I think we will be able to achieve this with a custom EventComponent, stacking #233 (that also allows ignoring overlaps) and custom styles per event #228

[rdewolff]

That's great. We have to update all the docs accordingly, as there are more and more features not visible in the main README.md.