[bug 959294] Remove sorl-thumbnail.
[bug 959294] Add sorl-thumbnail as git submodule.
Merge pull request #831 from glogiotatidis/959294

959294
[Fix bug 977556] Update version of python-memcached
Merge pull request #832 from caktus/977556-python-memcached-install

[Fix bug 977556] Update version of python-memcached
[docs] Update elasticsearch info.