Change Tos.version into a string

because the decimal format is kind of messy, especially we have:
1.01 != 1.1 and 1.1 == 1.10

Tos.version is now a CharField. For ordering, we use Tos.id instead
(the latest tos is the one with highest id).
1 job for 279-cgu-validation in 1 minute and 12 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
failed #219732
bootstrap

00:01:12

 
Name Stage Failure
failed
bootstrap Build
Step 7/7 : EXPOSE	25  143
---> Using cache
---> cacb460e7164
Successfully built cacb460e7164
Successfully tagged allgo_dev-smtpsink:latest
+ mkdir -p -- data/mysql
+ docker-compose run --rm dev-mysql sh -e -c 'if [ -f /dk/container_init ] ; then sleep 1; /dk/container_init ; fi'
error: db is already initialised
ERROR: Job failed: exit code 1