First steps towards a decent menu

# Progress

* [x] Place menu items on top
* [x] Add decent menu background
* [x] Make sure the header is above the menu background
* [x] Add burger menu icon
* [x] Add the most important menu items to the top bar (responsive fit)
* [x] Create slide open menu on the right side, interacting with the burger icon
* [x] Add decent side menu content