[Frosting:268] Quick fixes to LLViewerMenu

Fixes Stand Up slice not being hooked up in attachment menu
Translators, please update the pie menu accordingly. userdata="Translate,These"
Also fixes an instance where Continue Flying On Unsit would be ignored
[Frosting:288] Ability to left-click sit on one's own objects only.

Debug Settings DisableClickSitOtherOwner added.
Checkbox added to System Preferences for disabling click-to-sit on objects you don't own.

Also redid onCommitCheckBox a bit, best viewed without space changes.
There's more to this feature, but it doesn't work yet.
Fix a bug in the pie menu, in v3 there is a separate pie menu for others' attachments, we don't have this yet.
Made mClickActionBuyEnabled and mClickActionPayEnabled CachedControl members, so they can be changed without a restart.