Glens A, warnings and outputs

[Holmgren825]

This PR includes

• Warnings when user sets bad values for some parameters. Closes https://github.com/OGGM/oggm-edu-notebooks/issues/71
• AAR to glacier info. Closes https://github.com/OGGM/oggm-edu-notebooks/issues/62
• Enables the user to pass a temperature when setting the creep parameter A in Glens equation. The temperature is then converted to a creep parameter according to eq. 3.35 in The physics of glaciers, Cuffey & Paterson. See discussion in the issue. Closes https://github.com/OGGM/oggm-edu-notebooks/issues/72