idea is to transform ids of the form 'company:1:42', where company:1 is the owner and '42' is the company-relative id to separate columns owner and id,
where owner is a positive long for users and a negative long for companies.
however, as the id field would then only require a company-relative uniqueness, this currently cannot be done:
The legacy id filed has a unique constraint, which cannot be released in SQLite. So a new table will have to be created as an intermediate step.
Signed-off-by: Stephan Richter <s.richter@srsoftware.de>
