Add Xsp Properties editor from the ExtLib

[jesse-gallagher]

The 9.0.1-era xsp.properties editor from the ExtLib remains open source: https://github.com/OpenNTF/XPagesExtensionLibrary/tree/master/extlib-des/lwp/product/design/eclipse/plugins/com.ibm.xsp.extlib.designer.xspprops . Though it has a few native dependencies, I suspect that it wouldn't be too difficult to remove those.

[jesse-gallagher]

Hmm, I was a bit optimistic: though a lot of the Designer-specific bits are safe to remove, it looks like there's a bunch of proprietary com.ibm.commons.swt code used heavily. That's not necessarily the end of the world - as long as it's API-compatible, it should be doable to replace those, but it'll be a slog.