APIify and accept school parameter, with a school select-option. 

This PR will:
 * Add a selection-option element to index.html, which is easy to edit and add new schools to. 
* Will make phpProxy be able to get school id. 
 * Will make NOVA.js exportable, which means other developers are able to take this script and place it on their website. I did this by removing constants that was specific to index.html, so now, when you call ``NOVA.startNova()`` you will need to add a param for which DOM element the PDF should be rendered to. (We need to write some documentation for this).

All of this is placed in one whole PR because when I wanted to make school a prarameter, I felt like we needed to make it variable, which created the need to create an API, which in turn forced me to make the phpProxy able to accept the parameter. 

There you go! 

(I also deleted some code that was commented out of the script. Hope you don't mind)