Migrate to HTTP schema URI references for declared XML namespaces in our workproducts (here localsig profile)

In [Section 7 XML Namespace Identifiers and Namespace Documents of OASIS Naming Directives](http://docs.oasis-open.org/specGuidelines/ndr/namingDirectives.html#xml-namespaces) it says:

"""
An XML namespace name identified by an HTTP scheme URI reference must conform to the pattern: http://docs.oasis-open.org/[tc-shortname]/ns/xxxx
"""

and further on some exception to this rule:
"""
URN-based XML namespaces may be declared by existing TCs that have already used this feature, or by associated Maintenance Activity TCs, where architectural considerations require continued use of URNs. URN-based XML namespaces must not be declared otherwise, since they lack a standard, ubiquitous resolution method using DNS[+HTTP]. In URNs, the colon (":") character is expected.
"""
Allthough we for sure qualify as existing as well as maintenance activity TC, I suggest using the HTTP schema URI references for namespace declarations in our work products from now on.