Add new options

[mehmetb]

• Default dim level
• Action button behavior (dim immediately/show pop-up)
• Remove all tabs/this tab radio in favor of the dim level in the general settings. If the dim level is changed in a tab, it must be stored in the local tab state.
• Shortcut change through preferences page (*)
• Assign a mouse/keyboard shortcut to change the dim level (*)

(*): Might not be allowed by the web extensions API, need to check