Make necessary updates to load HXN data from tiled

[psavery]

For this, I tried to take an approach such that the relevant functions, such as map_data2D_hxn(), will run properly whether db is a v0 DataBroker instance or a v2 instance (which uses tiled). This would enable db to just be swapped out for a v2 instance when the time is right.

There is a variable is_tiled that tries to determine whether v2 is being used or v0, and some of the logic, in just a few places, branches based upon whether tiled is being used or not.

Some of the metadata needed to be accessed like start_doc['dimensions'] instead of start_doc.dimensions, but this appeared to work for both v0 and v2.

I realize this does not take into account the changes in #339. But I think the changes here are simple enough to take into account once #339 is merged.

These changes appeared to work fine with DataBroker v0. I had an example using DataBroker v2 that appeared to have the metadata, but not the data itself. I think it loaded and formatted all the metadata correctly, but there is a little uncertainty as to whether loading the data in to the pandas frame at the end is correct - that is something we can determine once we have a real example.