Adds the tagging system, with 3 types of tags:
* Calculator models grouped by compatibility classes
* Programming languages
* Game, tools, and course categories
[MIGRATION] This commit contains a new version of the schema.
[BREAKS] This commit breaks existing tag assignments.
[MASTER] Run the 'update-tags' command of master.py.
Not tested yet since there is a lack of tools to manipulate comments,
topics and programs. The /programmes routes is used to display a list of
all programs, temporarily.
Lephe
Darks