Support a configuration file

[toddpalino]

kafka-assigner should be able to support a configuration file to provide default arguments. This would be things like:

• Setting sizer selection and options
• Setting a default balance module list
• Default tools and JRE locations

The file can be looked for in a default location (e.g. ~/.kafka-tools) or specified on the command line (in which case it should be processed before the rest of the command line is).