Hidden functionality

Fix the start date of a task in the time tracker by requesting URL
/db/track_start/{time_track.id}/{desired_date Y-m-d H:i:s}. The
time_track.id value can be found in active tasks table (URL: /tracker).
There are no hyperlinks for /db/track_start/.
Modal fix

Some fixes in joined modals.
Multiple attachments #12

- Image list of returned values;
- Images and files in both task modal window and task editor;
- Modal CSS fix;
- Changed DB structure.