Make movable window class

[mterczynski]

window:
  always:
    - has a ma movable header
    - there's an "x" button in header on the right side
    - is movable after performing a mousedown on its header
  depending on window type:
    - if it's a popup: is has only the string as a title and "x" button in header
    - if it's not a popup: on the left side of the header there can by dynamic JSX, on the right side of the header there are also minimize and maximze buttons

[mterczynski]

Branch: 60-make-movable-windows