Tools for measurement

[Karry]

As @llaalleexxaanndd suggested at #319

The ruler in the lower left hand corner is already great, but sometimes you may want (at least I do) to get a quick rough view of distance in other directions than East-West. And you have to move endpoints down into the corner to make the measurement. I think that a (on/off switchable, like the collections star) big semi-transparent blob/circle in the centre of the map with the same diameter/scale as the length of the ruler in the corner would be a big help to give a quick view of the direct distance between two points on the map, in any direction.

Simple circle may be misleading with low zoom levels, because of distortion of Mercator projection. Instead, I would use selection of two points on the map...

I would consider to add extra entry "measurement" or "tools" to main menu with tools for measure distance and polygon area in square meters...