clock responsive to full screen + CSS for canvas

[FranzAT]

• clock size is responsive to full screen (mainly based on new #clock-section in CSS/main.css)

• update function draw() in file clock.js with canvas.width instead of fixed pixel values. Due to responsive design, also line weight or lengths must be responsive.

• get properties from CSS into Canvas with the help of DOM (mainly due to function getPropeties(className) in file clock.js). So that color and font of the canvas clock can be defined in CCS/main.css under #clockface

• set draw interval to 1000ms so that the second Hand is moving like a real clock.

• making 3 layers of the clock in index.html, so that additional functions can be added between clock background and clock hands (e.g. day/date)