Service enable

[danyspin97]

• [x] tt enable <services>: Enable service by parsing the file in tt directories (e.g. /usr/share/tt/service) and it to the current service database. <services> shall not be already enabled. The dependants of <services>, if any, will be reparsed again from the filesystem.
• [ ] tt enable --no-update-dependants <services>: Same as above, but use the dependants already found on the service database, parse the ones not found.
• [ ] tt enable --update <services>: Reparse the service if it is already enabled, fail otherwise.
• [ ] tt update-services: Reparse all enabled services and recreate the service database.