Update SLPF namespace

[Vasileios-Mavroeidis]

This is to capture that we need to update the namespace of the SLPF spec (in the SLPF spec). Presently, the SLPF spec, the Lang spec, and the architecture spec have 3 different namespaces for the SLPF spec.

[Vasileios-Mavroeidis]

I also attach the following, just in case.

http://docs.oasis-open.org/specGuidelines/namingGuidelines/resourceNaming.html

URIs for OASIS resources, as well as for HTTP scheme namespace URIs, should begin with the [exact, case-specific] 27 characters: http://docs.oasis-open.org/ unless specified otherwise by the OASIS TC Administration as an allowable exception