query builder wizard (a.k.a. ffs)

TODOs:

* [ ] error handling if search cannot be parsed or unsupported parameters are provided: show warning message right below input with some additional help text.
* [ ] regex vs. partial string search (`name~foo` vs. `name:foo`)?
* [ ] case sensitivity of regex searches?
* [ ] implement not-like `!~` operator
* [ ] allow `in bbox` bounds condition
* [ ] documentation