Is your feature request related to a problem? Please describe.
First of all thank you very much for your hard work, Xournal++ is an awesome app!
I've used Xournal++ on my tablet with a stylus for a few days now and I know that I can use the buttons on my pen to do a very similar thing but it would be great to have a way to select more pen properties at once, so that we can select more than N+1 templates real quick (where N is the number of buttons that our pen has + 1 for the tip).
For example if I want to write a title during my note-taking I'd use a thick red stroke, when I start writing normal text I'd use a fine black stroke, when I write questions I'd use a medium blue stroke, when I draw graphs I sometimes use a fine red dotted lines and so on.
If I only have 2 buttons and the tip I can only have 3 custom templates (and no place for the eraser), so for the others I have to enable every single property manually and this is sometimes time-consuming during lectures.

Describe the solution you'd like
It would be fantastic to have more quick-select fully customizable icons that can be inserted in the floating toolbar or anywhere else to have access to all the templates.