Add new features to config parser

[xylar]

This merge adds 2 new features to the MpasConfigParser:

• Config files can be written out in "raw" format, which preserves the config options that use extended interpolation, rather than substituting them. This is useful in situations where you want to write out a config file that can still take advantage of extended interpolation when it is read back in. Writing out in raw format is now the default.
• Two new methods, append() and prepend() allow you to add a copy of another set of config options either before or after a given set of options. This is useful for combining a set of specialize options with a set of common or default options, particularly if this procedure needs to happen repeatedly (e.g. for separate tasks, each with its own specialized options).

[xylar]

This work has been tested along with this Polaris branch: https://github.com/xylar/polaris/tree/add-shared-configs This testing exercised the new raw writing feature and the prepend() method.