Split Packages in scim-spec-schema and scim-spec-protocol

[Brian Demers <bd...@apache.org>]

There is a split package issue between the `scim-spec-schema` and
`scim-spec-protocol` modules
The `org.apache.directory.scim.spec.adapter` package is in both jars:

https://github.com/apache/directory-scimple/tree/develop/scim-spec/scim-spec-schema/src/main/java/org/apache/directory/scim/spec
https://github.com/apache/directory-scimple/tree/develop/scim-spec/scim-spec-protocol/src/main/java/org/apache/directory/scim/spec

One (or both) of these packages will need to be renamed to fix this.
Possibly renaming both of them to:
`org.apache.directory.scim.spec.core`
`org.apache.directory.scim.spec.protocol`

Another idea would be to merge them into a common `spec` project.
It looks like common usage of SCIMple would require both modules.  In the
source tree, the client and server examples require both packages.

Before going forward with anything, I wanted to see if anyone had insight
into why they were originally in different modules?  Is that just to align
with the two SCIM RFCs? (Protocol & Core Schema). Are there cases where a
developer using SCIMple would depend on `scim-spec-schema` and NOT
`scim-spec-protocol`? (Possibly someone packaging an extension model in a
standalone library)?  If so, is that common?

Thanks for any thoughts/ideas!

-Brian