implement timerange vef widget

this MR implements a method to configure widgets in the vef via the custom vefWidgets attribute in the JsonSchema.

see https://gitlab.awi.de/software-engineering/de.awi.visualexplorer/-/merge_requests/40/diffs?commit_id=f75033fbdeea19a0762f2ac2bc1b8d889b2288d5

ping @robin.hess