RF+BF - move scaling into new arraywriters module

Make new arraywriters module with scaling functions in class methods.

Refactor volumeutils scaling methods to use arraywriter scaling and
deprecate scaling functions in volumeutils.

Refactor array_to_file function to do a single safe clip of the data
either before or after applying slope, inter, with tests.

Make some tests of high-valued floats being converted to ints.

Author: matthew-brett