Lilac upgrade

Lilac has been released

With it, Tutor is now an officially supported installation method (and the recommended installation in the next version, Maple :O )

Release notes: https://edx.readthedocs.io/projects/open-edx-release-notes/en/latest/lilac.html

To do:

• Upgrade edx-platform fork
• Upgrade edx-search fork
• Upgrade tutor locally, go through upgrade procedure from README
• Update theme (indigo-totem!13 (merged))
• Update translations
• Test locally
• Test on staging (#64 (closed))