Action: Update parameter documentation

Return value of Action::getError always contains
a non-empty 'info' property, it hasn't been optional
for a while now.
ProjectAction: Move project creation logic out of cli script
dbUpdate: Add migration for 'users-projects-conversion'

Tested by installing master and project-4 in separate dbs.
Then checking out project-4 with the master database
configured and running dbUpdate.php.

Ran a diff on the mysqldump to confirm. Following diff has
become empty:

    $ mysqldump --skip-comments --skip-extended-insert --skip-add-drop-table --no-data -u root -p swarm_master > swarm_master_updated.skip.nodata.sql
    $ mysqldump --skip-comments --skip-extended-insert --skip-add-drop-table --no-data -u root -p swarm_projects4 > swarm_projects4.skip.nodata.sql
    $ diff -u swarm_master_updated.skip.nodata.sql swarm_projects4.skip.nodata.sql
    $