Refactor code to decouple datasetTypes from Database class

[kmdouglass]

After implementing generic types on #39 , I realized that all dataset types can be decoupled from both the Database and Parser classes. This would greatly make it easier to extend B-Store to new dataset types. It also really doesn't make sense to treat locResults, locMetadata, and widefieldImages as separate types from generics.

Since two of the main purposes of B-Store are to be extensible and to be easily understood when the databases are examined by humans, I should probably refactor the code at this point to completely separate datasetTypes from Parser and Database.

[kmdouglass]

The DatasetTypes are now refactored and most the HDFDatabase is as well. The last few steps will be

1. Remove DatabaseAtom and move its functionality into Dataset
2. Place the DatasetIDs into a private dict of Dataset.
3. Assign a function to Dataset that returns named tuples of only the fields requested by the Database
4. Redo the parser to work with the new Datasets

[kmdouglass]

All refactored code is now on the development branch.