Replaced MD5 with SHA2

I have rewritten the client side encryption by using [crypto-js](https://code.google.com/p/crypto-js/#SHA-2), because [MD5 isn't secure anymore](http://www.zdnet.com/blog/security/md5-password-scrambler-no-longer-safe/12317).

I don't know if this will do the trick, because I can't test it server-wise (I have no database available). 

I invoked the security code for:

*/content/login.php
/content/register.php
/content/verify.php
/content/handlers/register.php
/content/handlers/login.php
/content/handlers/verification.php*

Give me feedback, maybe I could improve some parts of my request! 

## Changelog (24.04.2014)

* removed MD5 script
* created a new security script
* globally included [jQuery](https://jquery.com/)
* locally included [crypto-js](https://code.google.com/p/crypto-js)