add TTL support for embedded Cassandra
Fixed TTL meta data to return 0 instead of null and convert to long.
cast ttl to primitive long for more efficient boxing
throw Unsupported exception instead of returning null in meta data getter for unsupported meta data.
Merge branch 'embedded-ttl' of https://github.com/thinkaurelius/titan into embedded-ttl

Conflicts:
	titan-cassandra/src/main/java/com/thinkaurelius/titan/diskstorage/cassandra/astyanax/AstyanaxKeyColumnValueStore.java
	titan-cassandra/src/main/java/com/thinkaurelius/titan/diskstorage/cassandra/thrift/CassandraThriftKeyColumnValueStore.java