allow legacy ssl connection
use MongooseIM 1.5.0
change ssl option to starttls
Change variable names
Merge pull request #52 from esl/ssl-connection

allow legacy ssl connection
allow to specify outgoing interface
fix lookup stanza
changes related to mam v0.3 update
don't create xform when it is unnecessary
Add disco_items/2
allow to automatically drop messages
filter out stanzas based on drop_pred
introduce escalus_connection:get_stanza/3 with timeout as the last arg
rename drop_pred to filter_pred

the logic is also reversed
introduce escalus_connection behaviour