Start vanilla j2se implementation as a copy of android impl
j2se: Rename files to Impl
j2se: change package name in class files
j2se: update code with renamed classes intra-package
j2se: generalise PlatformImpl
j2se: adapt to simple HashMap-backed storage for testing (must use persistent storage for real impl)
Rename androidFactory to platformFactory
Remove Android-specific contact support (no longer supports any contact backend)
Add vanilla logging capability for J2SE
Remove hard-coded references to ZBC provider, use BC provider as default, import org.bouncycastle instead of zorg.bouncycastle
Remove hard-coded references to ZRTP default HMAC auth tag size, support configurable values
Add volatile flag to ZRTP state
Further generalise the way authentication tag mode/size is selected
Convert CipherType into an enum type.  More thread safety improvements (queue the messages for processing on single thread).
Add method to discover selected cipher type
Further fixes relating to the change of CipherType to an enum
Allow client to discover if ZRTP is in progress
Dynamically support key sizes according to selected cipher type