Remote useless qlc.hrl from mailbox
Fix erlang:monitor/2 race condition that caused multiple delivery of messages on incorrect {'DOWN', _, _, _, noproc}
Pick the right {gateway_id, output_message_id} message using latest datetime.

The problem is when SMPPSim is restarted it starts to deliver output_message_id starting from 0. This way an inconnect
message would been selected using just {gateway_id, output_message_id} index. This is fixed by previously sorting
all [{gateway_id, output_message_id}] by descending order and then selecting the first one.
Refactor connection record

The connection is a distinct SMPP primitive that describes a SMPP connection.
SMPP full fields name should be used. Also bind_type should contain atoms
transmitter, receiver, and transceiver. Http api should also force meaningfull
bind_type parameter value like transmitter, receiver, and transceiver.
Add xref
Remove mailbox gcollector. Cleanup
Review internal data structures. Cleanup
Fix crash, caused by wrong patter matching
Reduce warnings. Add specs. Update deps
Update mailbox deps
Update http app to support recent gen_http_api version
Add simple-test for travis-ci
Add more tests to simple-test target
Replace behaviour_info callback with callback attributes
Fix ?gv and tests
Fix script
Update docs
Update docs
Update networks to make it possible to test against SMPPSim DeterministicLifeCycleManager
Prettify date