Introducing _distance_point_box and _closest_box


git-svn-id: svn+ssh://svn.code.sf.net/p/mcomix/code@956 ef8490bc-f317-4725-81ed-e95a9aca1bcf
Introducing Box, refactoring, bug fix

closest_boxes now returns the indices of ALL boxes that have minimum distance


git-svn-id: svn+ssh://svn.code.sf.net/p/mcomix/code@957 ef8490bc-f317-4725-81ed-e95a9aca1bcf
Introducing viewport_center, bugfix


git-svn-id: svn+ssh://svn.code.sf.net/p/mcomix/code@958 ef8490bc-f317-4725-81ed-e95a9aca1bcf