OGGM glacier directories url need an update

[fmaussion]

Reported by @gillian-smith :

igm/igm/inputs/oggm_shop/oggm_util.py

Line 50 in e57e31a

base_url = ( "https://cluster.klima.uni-bremen.de/~oggm/gdirs/oggm_v1.6/exps/igm_v2" )

Do not exist anymore - will try to do this tomorrow.

[fmaussion]

I just created a new URL for RGI6 with ERA5 data: https://cluster.klima.uni-bremen.de/~oggm/gdirs/oggm_v1.6/exps/igm_v5_era5/

I did ERA5 instead of W5E5 because I thought this might be more popular amongst IGM users. I'll start a quick "poll" amongst the IGM community about the following questions:

• ERA5 or W5E5?
• an option in IGM itself to select one of both?