Create "mixin" class for common Thinker patterns

[WardLT]

Many of the Thinkers I write share common patterns, such as a output directory in which I write log files.

We should create Mixin classes that one can add to their thinker which add these features. For example, I could create one which provides a method that saves a Result object to the output directory.

[WardLT]

Another common pattern could specify logging and visualization tools. (We could bring this home from the 'reporters' in ExaMol)