Measurer - Add Select Feature

[OlofSvahnVbg]

As mentioned in previous issues (#1311), there should be a select feature in Measurer.
Similar to the one that already exists in Sketch:

The function could be accesed via a button that would - preferably - sit in between the circle and delete button:

This would enable selecting of a active feature. Clicking this feaure would then automatically measure its circumference using the appropriate measurement (polygon, line, etc.)