modules/rtpproxy: Add database support to rtpproxy

- If db_url modparam is set rtpproxy sets will be loaded from database
- If the instance is marked as disabled in database it will be loaded as disabled

- Currently no persistence (enable/disable MI command does not affect DB)
- Loaded during mod_init - cannot be reloaded at runtime (as before)
modules/registrar: changed instance related INFO to DBG
lib/srdb1, kamctl: Add new rtpproxy db table to schema
Merge branch 'master' of ssh://git.sip-router.org/sip-router

* 'master' of ssh://git.sip-router.org/sip-router:
  modules/registrar: changed instance related INFO to DBG
modules/stun: STUN module

- Based on ser_stun.[ch]
- No longer a compile time option in Kamailio core
modules/stun: Module documentation for STUN
core: removed ser_stun.[ch] from core

- STUN now in a module
core: removed STUN from core

- Added hooks so that STUN messages can be passed to a module
- Removed STUN configuration file parameters
core: Updated modules list in Makefile.groups to include stun
modules/outbound: updated to reflect STUN being in a module now
pkg/kamailio/(centos|fedora): Updated .spec to build new stun module

- Also updated rel to dev1
modules/stun: removed unnecessary include
modules/outbound: updated edge proxy example to use STUN module
modules/outbound: cache decoded flow-token in sip_msg structure

- Saves multiple OpenSSL calls if the same flow-token is needed in more
  than one place
modules/rr: updated because outbound:decode_flow_token() arguments changed
core: added structure to hold cached decoded flow-token to sip_msg structure
modules/outbound: fixed segmentation fault
modules/rr: fixed outbound related segmentation fault
modules/outbound: changed some INFO level output to DBG
stun	Add clarification to the README

And a big thank you to Peter Dunkley and Crocodile RCS for doing the
work involved in making this a module, instead of a compile time
options. Modules are cool. And easier to handle by pre-compiled
distributions/packages.