join points, break path) and fixed KoSubpathBreakCommand while at it.
Some additions and changes to make them work:
* added default constructor to KoPathPoint
* added a function to KoPathShape to return a subpath of a given point
* added function openSubpath to KoPathShape which uncloses a closed subpath
* changed KoPathShape::joinBetween to keep the older subpath when
  merging two subpaths
* KoSubpathBreakCommand now stores the data of the whole subpath
  before breaking, which fixes the broken undo behaviour
* KoParameterToPathCommand can now work on multiple shape at a time


svn path=/trunk/koffice/; revision=614492