Completely new template.

This request changes the following things:

- template has been renamed to `default.html`
- variables have a new syntax `{variableName}`
- added added new styling and moved everything to `style.css`
- labels need to get the color from the api call assigned to the `{color}` in the style attribute on the bg tag

I think we should go for a different logic:
1. get data from api
2. render all elements with data (maybe use data-labels, data-milestone and data-id) 
  2.2 only the elements with the class visible are actually visible
3. Instead of the js building elements on the fly, it just finds the correct elements (using the data-) and adds the visible class to those.

We should stick to your no-framework idea, since we just need to use `getElementByClassName` to get the and can add/remove the classes using the `classlist` api. (Can you move all the js to a separate file, which would make changing and debugging a lot easier).

- Labels and milestones should be deselected when clicking on a selected item.

Closes #6 #2 

@jreinhardt you think it you can work with this?