Spinner: compress geometry tracking

not necessary while invisible nor more than once per
event cycle (esp. not on every single invalidating incident
of any ancestor)

REVIEW: 112239
www: list the Windows binaries maintained by Christian

REVIEW: 112222
Make sure that Common::SettingsNames:* are const

These are only initialized once and have no reason to be modified, ever. Thanks
to Pali for reminding me that they are not const at this point.

REVIEW: 112284