Implemented Seach Singer and modified search item a bit
Noticed that manager can reduce stock to negative.

If manager tries to reduce stock it is okay.  If it turns out that stock
will go below zero just set the stock to 0.
Merge pull request #23 from ellina-s/arjan

Noticed that manager can reduce stock to negative.
Populated Table for the current date
Merge pull request #24 from ellina-s/arjan

Populated Table for the current date
Implemeted precise item search
Added search by category or title, and search by singer name
Added search for duplicates
Removed duplicates from search results
Added checks for nulls
Refactored helper methods in a helper class
Merge pull request #25 from ellina-s/ellina

Ellina
Merge pull request #26 from ellina-s/clark

Clark