Beginnings of making Slot#top work

* unslot the Slot (e.g. absolute positioning) if left or top are
  supplied
* refactored so that current_positiong starts straight with
  margin_left and margin_top so they don't have to be added in
* removed explicit top/left from top slot (not needed)
Call contents_alignment once evaluing the block is finished

* then elements are already correctly positioned
* the unslot approach is not totally right (refer to #217)
  but better than what we have so far/a step in the right direction
Add the left margin when moving to a new line

* fixes #164
fix test failure
Some margin specs for slots
the console is actually opened via alt_/ not control
Refactor color handling in Swt::TbPainter

- extract method for creating SWT colors with defaults
- Refactor foreground, background colors
- add specs
Add specs for Shoes::TextBlock with nested fragments
Game of life sample by @fuksito
Merge branch 'master' of github.com:shoes/shoes4