FCPInterface: Simplify mechanism of DeprecatedFields once more

Instead of putting them into an own SFS key
"DepractedFields=Field1,Field2,..", have a key for each one
"Field1.DeprecatedField=true", ...
While this takes more space, it will simplify the following commits
which deprecate a lot more fields: They shall change functions such as
addIdentityFields() which only know a specify index of a field, for
example "Identities.5.Nickname". So they couldn't easily put the
"Nickname" field into the deprecated list because they don't know the
version of the prefix "Identities.5" without the integer 5.
FCPInterface: Fix documentation to say "deprecated" instead of "legacy"

This matches the standard "@Deprecated" of Java and thus will cause
developers to not miss those deprecated items anymore when searching for
"deprecated".
FCPInterface: Organize imports