Breadcrumb width calculation fix

Rewrote the breadcrumb calculation to be more readable.

Breadcrumb now has a setMaxWidth() method to set the maximum allowed
width which is used to fit the breadcrumbs.

Fixes https://github.com/owncloud/core/issues/9115
I removed the debounce because it made the UI jumpy, sometimes the actions bar would shortly wrap.
But you're right, performance is more important.