Changes:
Rework integration tests
New structure of base integration test classes
bump dependency on signal-protocol-java from 2.4.0 to 2.6.2
Introduced CachingOmemoStore implementations
Use CachingOmemoStore classes in integration tests
Removed OmemoSession classes (replaced with more logical OmemoRatchet classes)
Consequently also removed load/storeOmemoSession methods from OmemoStore
Removed some clutter from KeyUtil classes
Moved trust decision related code from OmemoStore to TrustCallback
Require authenticated connection for many functions
Add async initialization function in OmemoStore
Refactor omemo test package (/java/org/jivesoftware/smack/omemo -> /java/org/jivesoftware/smackx)
Remove OmemoStore method isFreshInstallation() as well as defaultDeviceId related stuff
FileBasedOmemoStore: Add cleaner methods to store/load base data types (Using tryWithResource, only for future releases, once Android API gets bumped)
Attempt to make OmemoManager thread safe
new logic for getInstanceFor() deviceId determination
OmemoManagers encrypt methods now don't throw exceptions when encryption for some devices fails. Instead message gets encrypted when possible and more information about failures gets returned alongside the message itself
Added OmemoMessage class for that purpose
Reworked entire OmemoService class
Use safer logic for creating trust-ignoring messages (like ratchet-update messages)
Restructure elements/provider in order to prepare for OMEMO namespace bumps
Remove OmemoManager.regenerate() methods in favor of getInstanceFor(connection, randomDeviceId)
Removed some unnecessary configuration options
Prepare for support of more AES message key types
Simplify session creation
Where possible, avoid side effects in methods
Add UntrustedOmemoIdentityException
Add TrustState enum
More improved tests
