Improve GridLAB-D data parsing for datastore

[trevorhardy]

Though HDF5 files can have arbitrary schemas, since we use GridLAB-D a lot its probably worth setting up a dedicated parsing path that totally re-works the DataFrame before giving it to the user. The name of the files produced by GridLAB-D are hard-coded so we should be able to easily detect when an HDF5 file is of that format. Features we should probably include:

• Concatenating data from all days in the file into one table. Data is currently split up by day into unique tables "index1", "index2, ...
• Making unique tables for each object in the table. Right now all objects are aggregated into one table which creates non-unique values in the table (all of the objects have a row with a given timestamp). Separating out each object into a table allows for indexing which is a good thing.
• Index each table by the timestamp
• Define data types for each column in the table. These are known as the output from GridLAB-D that creates this HDF5 is static (takes a source code change to adjust).

This will result in a lot of unique tables BUT they will all be easy to work with.