Keep sstable level when bootstrapping

Patch by marcuse; reviewed by iamaleksey for CASSANDRA-7460
Remove UDF-as-class functionality

patch by snazy; reviewed by slebresne for CASSANDRA-8063
Merge remote-tracking branch 'origin/trunk' into 7563v3-udf-types

Conflicts:
	src/java/org/apache/cassandra/cql3/functions/ReflectionBasedUDF.java