Custom intervals in ScalebarBlock

With this improvement we added two new configuration parameters to !scalebar blocks that allow to customize the scalebar preferred bar lengths.

By default these were chosen in the 1,2,5,10 set.

Now this set can be customized using the preferredIntervals property. This property is an array with the new (integer) allowed lengths.

Another property, preferredIntervalFractions, can be specified to also use fractional intervals. By default only 0.0 is used, and thus only integer lengths are allowed.

Example

preferredIntervals: [1,3,5,10]

preferredIntervalFractions: [0.2,0.5]