added de-/serialization of multi sub-keys of QblPrimaryKeyPair
added de-/serialization of multi sub-keys of QblPrimaryPublicKey
added multi sub-key support to class Contact:
- new getter for retrieving list of sub-keys
- marked old getter @Deprecated
- changed name of sub-key setters from setX to addX
changed modifiers of generateEncKeyPair() and generateSignKeyPair() to public
changed contactTest() for testing multi sub-key serialization
changed syncedSettingsTest() for testing multi sub-key serialization
Merge pull request #219 from f-porter/Issue-206-add-multi-sub-key-serialization

Issue 206 add multi sub key serialization