Various fixes to GeoDataset

[adamjstewart]

This PR contains fixes to various bugs I've discovered so far in GeoDataset and its subclasses:

• Landsat: regex now correctly matches B11 filename
• Landsat/Sentinel: globs now match a single band per scene instead of adding every band to the index
• RasterDataset: fix shape mismatch errors when trying to concatenate bands of different resolution (Resolution/resampling #74)
• RasterDataset: fix sampling outside of the bounds of an image resulting in a smaller tensor instead of nodata values
• RasterDataset: merge overlapping files
• VectorDataset: merge overlapping files

There are also tests to prevent regressions.

Fixes #74

[calebrob6]

I didn't review this thoroughly (am mostly out until Thursday) -- feel free to merge if you are confident

[adamjstewart]

Confident that it doesn't introduce any new bugs? No.
Confident that it has fewer bugs than we had before? Yes.