Should resolve #402 (only for cicular beds)
Merge branch 'devel' into nullie-circular-beds
Small adjustments to #407

- Refactored drawGrid into two functions drawRectangularGrid and drawCircularGrid
- Made sure grid for circular beds always "starts" at (0,0) so that e.g. for a radius of 105mm the center of the bed will be on the grid lines
- Made center on circular bed be better visible by making origin lines thicker
- Made initial focus on bed center properly
Merge branch 'devel' of github.com:foosel/OctoPrint into devel