[PATCH] Draw Tools should look disabled if non-drawable Layer is selected

[xeen]

The motivation is that new users have an additional clue why draw won't draw when they've selected a different layer (i.e. Validator). I experienced this quite a lot when I was still new to OSM.

I tested it with also disabling actions (currently just the buttons look disabled) but found it annoying that my tool was being unselected when moving layers and also found that I switch layers while I switch tools (by using mouse and keyboard) and it was annoying to have to mind order.

The patch implements a general method of binding tools to layers. In my opinion this should be used for the "move WMS Layers" tool (which needs fixing anyway because it moves a "random" layer if there is more than one WMS layer).

[xeen]

Fix for WMS plugin as suggested

[anonymous]

Applied in r1379.