Fixes for my two issues

couchbase/couchbase-lite-android#108 and couchbase/couchbase-lite-android#94

Put a boolean on CBLAttachment to indicate whether it is gzipped or not, with a getter and a setter.
Added a way to test whether an attachment is gzipped.
Replace UUID's after a database copy.
Parse out content-encoding correctly. Support for 'gzip, deflate' values.