Basemaps downloading requires a timeout option

[pabloitu]

Querying a webservice for basemaps requires to have a timeout specification

pycsep/csep/utils/plots.py

Line 2727 in 5f84ea9

def _get_basemap(basemap):

so it can default to stock_img and does not freeze runtime of there is any connection problem.

The download time of a basemap can be significant (2-20 sec). However, many times it is required to plot the same catalog (or the same region) multiple times. It would make sense to cache the download basemap.