Add a global options dialog

[arantius]

Tools>Add-Ons>Greasemonkey>Options used to open manage scripts dialog. That dialog is now (as of #1086, for version 0.9) a tab in addons. This options window should now become a place to set global options regarding greasemonkey, and not given scripts.

This dialog needs to assume the "uninstall preferences with scripts" option lost from the old manage scripts dialog. I'd prefer it to default to on.
This dialog can also, eventually, include a place for the settings to back #1002 and #1012.

[Martii]

+1 for defaulting to on for uninstall associated preferences.

[arantius]

Done in f30c1b3 and 0ac9e9a.