WIP (failing): add support for receiving single elements of lists

weird bug, that causes errors when nonterminal A (in the singleList-test) has no children.

- uri-parsing: include fragment for mqtt wildcard "#"
- MqttHandler
  - remove static imports
  - support wildcard callbacks
  - address compiler warnings
  - wait for successful connect and disconnect (and only then return true)
- add separate connect methods to connect using wildcards (for single-element-non-withAdd)
- test for single-list
  - reversed order for connecting send endpoints
  - fixed assertions
  - remove B from grammar and test