Add. Ctrl+Click toggle bookmark

[moteus]

[pkulchenko]

I know it's a simple change, but I don't think it's the right way to approach this, as I'd prefer to implement a more general solution, which will allow to link different margin clicks to appropriate actions (referencing MarginMarkerClick, MarginFoldClick, MarginLineNumberClick, and so on).

I don't have a full solution yet, but I expect to have something workable next week.