Responsiveness

### Change log
+ The site is responsive on all pages
+ Tidied up the css a bit by reorganising some things ( e.g. some of the css related to the portfolio was all over the place so i moved it all together )
+ Redesigned the header for a more organised look and for easier responsiveness
+ When on screen sizes < 768px the navigation bar is replaced with a slide in

### Things need changing
+ Currently there are two nav menues one for the main navigation and one for the mobile, I (Tom) needs to rewrite the javascript so that there is only one navigation menu for improved efficiency and help with adding/removing pages.