Added default price setting, some fixes
+ Gear button in the action bar now shows a setting screen where you can set
  your preffered price to be displayed on the plan
+ Changed comments layout a bit
* Fixed plan going back to the current day when the screen orientation is
  changed
* Changed comment button label on meals if there are no comments yet
* Fixed price display showing 0,00€ on side dishes and meals with unknown
  prices
Fixed litte comment bug
* Fixed each comment showing the same date and time in CommentFragment