remove ejabberd_cth module from source

It is meant to be used in tests so src directory is not for it,
moreover this module is never called
remove snmp related modules
remove p1_* files they are downloaded as one dependency

rename p1_fsm to p1_fsm_old and use in ejabberd c2s
refs #291
do not use p1_mnesia as it no longer exist
remove legacy offline odbc backend
allow compression on default c2s port
Merge pull request #328 from esl/improve-code-coverage

Improve code coverage