add abstract implementation meta-data field
move deactivated Uid into implementation meta
support tracking existing objectClasses and adding any required ones that are missing
always update objectClasses
relayAttributes should always be set on users
remove cruPersonAttributes if the user no longer has any of the Cru Person attributes
document that the *ImplMeta methods are for internal usage only
fix a NPE when a CN doesn't exist in the LdapEntry

also remove valid looking email check
test to ensure we don't accidently remove future objectClasses
only update objectClass when attributes depending on a custom objectClass change

also disable removal of cruPersonAttributes until post-merge