Recovery, bindings, ioclient and ioserv improvements

* Added ability to stick session to specific address by introducing new API: `session::set_direct_id()` and `session::get_direct_id()`. Pass them to cpp and python bindings;  
**NB!** This change breaks ABI.
* Now that we have proper API for sticking session to the particular address we can remove old workarounds for merge;
* Unblock `SIGTSTP` and `SIGQUIT` in `dnet_ioserv` for ease of debugging;
* Fix error message in `dnet_ioclient`;
* Misc formatting and documentation fixes.