Added the option to retry if server errors occur
Added the option to retry if server errors occur

Added additional redundancy by retrying download if there's a server or
connection error.


Former-commit-id: 0ccb6c61245e761491084a78b342dae53ceaa95b
neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox,neuropoly/spinalcordtoolbox