[ssn] rebuild/restructure/redesign/modularise ssn: call for proposals

SDW-ers
As discussed (again!) in the meeting today there are several proposals on the table for redesign of the ssn-xg ssn in one way or another. These proposals are variously  called "modularisation", "alignment" , "extension", "simplification", "core" , "skeleton"  etc.  Some are scattered around our wiki already; others have been raised in meetings or briefly on the mailing list  but are not well recorded.

I invite you to submit your proposals by recording them on the wiki page I just created here
https://www.w3.org/2015/spatial/wiki/Proposals_for_rewriting_SSN
and anchored on the wiki main page in the SSN section.

This is intended to give a persistent and written account of the proposals that the meetings can then take on board in well-informed discussions as we move towards a decision. As agreed (again!) in the meeting today this will not be resolved for the FPWD but I hope that a robust and informed discussion can be held *after* the FPWD is published.

There is also a question about whether these proposals should be even  "*mentioned*" in our FPWD. I'm ok with that in the form of a sentence or two marked as an issue. Please feel very free to propose that "sentence" in your proposal too.

Timeline? I am not certain but I imagine this will be the highest priority after the FPWD is published; so maybe a month from now?

--Kerry