Revert "temporarily remove document cache from Database"
Revert "temporarily remove document cache from Database"

This reverts commit f1f8b94ecf9d1d1aa84fa1395927b746eca02b44.

Spotme/couchbase-lite-java-core,gotmyjobs/couchbase-lite-java-core,deleet/couchbase-lite-java-core,4u7/couchbase-lite-java-core,couchbase/couchbase-lite-java-core,mariosotil/couchbase-lite-java-core,netsense-sas/couchbase-lite-java-core,mariosotil/couchbase-lite-java-core,mariosotil/couchbase-lite-java-core