Convert base-line BlueSky model loading functions

[hmrtn]

Some low-level functions need to be converted to support the new raster package direction. At the very least, our top-level load function will need a rewrite, but we should also explore improvements at the others.

• [x] Explore bluesky_download() to look for potential improvements.
• [x] Explore bluesky_toV2(), ditto
• [x] Rewrite bluesky_load() to support loading via the raster package.

[jonathancallahan]

A few suggestions:

bluesky_download()

• Let's change the quiet parameter to verbose (and invert logic) -- that seems much more common.

bluesky_toV2()

• seems OK

bluesky_load()

• Keep a verbose parameter so one can observe progress
• Handle either xlim, ylim or a bbox parameter (Several examples of bbox use are found in the MazamaSatelliteUtils)
• Note that the timesteps argument is used for aggregation "chunk"ing
• Keep in mind that we want to use NetCDF data access capabilities to minimize the amount of data we have to load into memory.