(DRAFT) Added many configuration options to the dock and the panel

[AKArien]

• Dock and panel :
  • Changed « Autohide duration » to « Animation duration »
  • Added options to control the delay before doing the showing/hiding animations
  • Added options to place them on the left or right edge of the screen
    • This also includes an « orientation », that allows to override how certain elements might want to change depending on the position. For the dock, this can show the icons with their « base » oriented to an edge of the screen. For the panel, most widgets now have a layout optimised for a vertical bar.
• Dock :
  • Added dock width option
  • Added maximum entries per line. When this number is exceeded, a new line is created for the next icons.
• Panel :
  • Renamed « Widgets left » and « Widgets right » to left/top and right/bottom to go with new option to have panel on the sides
  • Added minimal width option
  • Added option to let the panel not span the full edge
    • Option to force the panel to be centered by the middle box instead of the total width. This will lead to more spaced out elements in the side that takes less space

Adresses #259