This commit changes the search box up the paginator, and fixes a security problem.
ATTENTION! The version which has search box MUST update to the newest version IMMEDIATELY, the old version did not process the escape of the string, may cause SQL injection problems.
Add a search box on problem set page. Only uses a simple algorithm, you can't use it like Google. You can search one or some of the words in the title.
NOTICE: The style of the sarch box may have some problems. when you turn the window into mobile mode, the search box will not be at the center of the page. Hope someone can make it better.
