Add import/export in console

[NicolasCARPi]

In this PR:

• bin/console db:install is replaced with bin/init db:install because at this time the config table doesn't exist and it messes things up. Old command still exists and simply inform about the new command.
• the commands namespace is now mostly tested
• add missing item_count to team_tags GET api v2
• remove the old index.php at root, this was a guardrail during update to 2.0.0 back in 2018
• add bin/console items:import/export users:import/export. It is named users:` but exports experiments in .eln. This allows exporting without running into timeout issues for bigger exports
• rework some code for cache:clear command
• better handle the status of experiments during import: try to match with existing status
• get rid of the logged warning during unit tests with Tex2Svg
• add a getPath() to Storage
• use the AsCommand attribute for symfony console commands (static property was deprecated)