Replace the Setting Mod symbol with a Plus sign

The SWADE ruleset in generally follows the convention that the "Dragon Symbol" represents a link and the "Plus Symbol" represents a sub-window that can be used to enter additional modifiers. Examples:

- Skills have the dragon symbol and link to the corresponding skills
- "Race" has the dragon symbol and links to the race that has been dropped there
- "Pace" has the plus sign and can be used to enter modifiers
- Next to the Rank there is a plus sign that opens the character summary

The only thing that deviates from that is "Setting" under the main tab. There, a dragon symbol is shown, but no link can be placed there - it's actually a subwindow to enter setting modifiers.

It would be nice if that could be brought in line with the rest.