Consider upgrading sorl-thumbnail when available

[vkurup]

There are some deprecation warnings being issued by Pillow, which are caused by sorl-thumbnail. There is a new sorl-thumbnail release on github, but it has not yet been released to PyPI.

Note that I haven't tested the new release at all, but just wanted to leave a placeholder ticket to remind someone to consider it.

[camilonova]

Just released https://pypi.python.org/pypi/sorl-thumbnail/12.4.1

[vkurup]

Thank you for notifying us!