Search function

This branch adds functionality to the search bar, which has been present at the top of the every page. When user writes an input and clicks "Search" button, user is taken to the index page. The item listing shows now only those items, which has the search word in their title or description. Search is case insensitive. All special characters are removed from the search word before the database query, since some characters are illegal and will cause crash. For example: '&testi=oho' -> 'testioho'.

Also as a small change: when user logs in, they are redirect to the index page rather and register page. Added this change because it was bothering me.