Switch to dict instead of ordered dict in Vizier find_catalogs about astroquery

[keflavich]

I'm onboard with both changes.

[bsipocz]

Yeap, both sounds reasonable.

[ManonMarchand]

So, this motivated #3028 which will make find_catalogs way faster. However, switching to a dictionary will remove the possibility to do this (in the docs here):

from astroquery.vizier import Vizier
catalog_list = Vizier.find_catalogs('Kang W51')
catalogs = Vizier.get_catalogs(catalog_list.values())
print(catalogs)

Where we use values instead of keys. So that's actually a change of API. Maybe not such a good idea.