Adds a die(); function after every header call

-Earlier the header function was not being stopped or exiting from execution, so the script will be executed till the end, and can cause some unexpected behavior. Therefore, now using a die() after every header() of “Location” to close the connection
Installer now uses MySQLi
Correct check if database exists (and option to clean it before installation)
Added the exhibition mode, if the flag is set in the configuration file, then you put any credentials in the login page and the Guest user logs in, it's a fully functional normal user. If the user is not part of any classes you run the script HACKADEMIC_INSTALL/misc_scripts/add_Guest_to_every_class.php to add the Guest to every class

Signed-off-by: Spyros Gasteratos <morfeas3000@gmail.com>
Merge branch 'fixUndefinedVars' of https://github.com/ankitashukla/hackademic into ankitashukla-fixUndefinedVars

Conflicts:
	challenges/izon/logout.php
fixed the db a little

Signed-off-by: Spyros Gasteratos <morfeas3000@gmail.com>
Merge pull request #74 from MisterIcy/installer

Installer now uses MySQLi