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

TODOs:

* [x] error handling if search cannot be parsed or unsupported parameters are provided: show warning message right below input with some additional help text.
* [x] ~~catch unsupported boolean logic (xor, except)~~
* [x] regex vs. [partial](http://stackoverflow.com/questions/5663987/how-to-properly-escape-characters-in-regexp) string search (`name~foo` vs. `name:foo`)?
* [x] case sensitivity of regex searches?
* [x] implement not-like `!~` operator
* [x] allow `in bbox` bounds condition
* [ ] documentation