Update astropy.coordinates.EarthLocation.of_site for Lowell Observatory sites about astropy-data

[eteq]

The DCT change is easy I think - we can change the "canonical" name for the-telescope-formerly-known-as-DCT to "Lowell Discovery Telescope", but have "Discovery Channel Telescope" remain as an alias?

lowell is trickier in that it's possible that some users are depending on that being consistent with past codes. The main reason I have that worry is that it originally came from the IRAF database (which explains why it's so old...). So here's an idea:

1. Make NPOI (or whatever that stands for - I think it's "Navy Precision Optical Interferometer"?) as the "main" name for what's currently lowell, and add any aliases you also think might make sense with that name.
2. have "lowell" be an alias for that entry
3. add "Lowell Mars Hill" and/or "Lowell Main", "Lowellobs" and/or similar for the Flagstaff location.
4. (this may require a code change in astropy) - have any request for just 'lowell' raise a deprecation warning that the name is now ambiguous and shouldn't be used in future code.

or alternatively we can just do as you suggest, which is just doing 1 and 3 and having "lowell" be an alias for 3.

I might be over-thinking this, though - I don't actually know that anyone is using the NPOI "Lowell"... But since it's in large part likely to impact Lowell users, @joellama, I'm wiiling to just accept whichever you think is best.

[hamogu]

That's been done in #121.