Add Icons for Map Center and Mouse Center

[dpaulat]

Add icons for the map center and mouse center.

• Map center icon should have an enable/disable selection in the Map Settings (Radar Toolbox), and be displayed in the center of each map
• When holding SHIFT, the mouse icon should display on each map that does not have the mouse hovered

[acidhorse1972]

when doing the crosshair cross you can use an inverted color + opacity aka alpha channel level and allow for details underneath to show thru such as reflectivity or base velocity etc

[dpaulat]

when doing the crosshair cross you can use an inverted color + opacity aka alpha channel level and allow for details underneath to show thru such as reflectivity or base velocity etc

I plan to make icons customizable in v0.4.5 (#145), which will allow for both a user-supplied icon, as well as custom transparency or changing/modulating the color. For now, the icons are small. I'll be creating a pull request for this shortly.

Map Center (enable in settings):

Mouse Coordinate: Yes, this one is very small, but unobtrusive and fairly noticeable when in motion. You can enable this by holding "Ctrl".