bypass scale locking to available factors

This pull provides an option in config.yaml to bypass the "locking" of scale to the available factors listed in the scale block. It simply takes the suggested value as passed to getBestScale produced in MapBlock.java.

This option, "disableScaleLocking", is of course false by default.

One of the applications I have been working on deals with a extremely wide range of scales that may be used, and I needed this functionality to avoid creating thousands of relevant scale numbers, which in my testing, prevents Mapfish-Print from operating.