Enhance Metadata to handle multi sample measurements and buffed out comments

[micahjohnson150]

@jomey @micah-prime @aaarendt and I spoke recently. Two big changes will affect the metadata parsing were concluded.

1. Multiple sample columns (density_a, etc) will be eliminated and instead directly uploaded as value.
2. Flags are going away also and being added to the comments.

The work to begin with is going to split up the snowex variables into snowex primary variables (ones we will upload as 'value') and snowex meta variables (supporting information i.e. date, lat long, comments etc). This split will take place in two repos. insitupy will host the bases of these classes and snowex db will extend them.

This distinction will help us make decisions between things like samples a,b,c and enhancing comments. It will also make it easier (and clearer) to add variables as datasets become available.

The branch for insitupy is https://github.com/M3Works/insitupy/tree/snowex_v2_work

@micah-prime is taking the implementation of the primary variables and I will take the metadata ones.

Once we get these in place I think we can start to divy up tasks. Let me know if you have questions/comments.