- added correct selection attribute to properties-editor
- started laying out the basics for a generic properties editor
  * will need to handle any properties available in a selection
shape / part
- added back mesh export, this time using the dedicated custom element
- fixed a few selection related issues
- fixed numerous issues with importing meshes:
 * hierarchical formats (amf) importing now actually gets the whole
object hierarchy
 * fixed offseting issues when importing hierarchies
 * still needs rotation & scale handling
 * all these fixes are semi temporary: once data structures
are frozen , these will need to be put into the parsers/loaders
themselves
- improved "snapping" for transforms:
 * rotations are now settable in degrees, not radians (simpler for now)
 * all snapping settings are automatically set on program startup
-de activated connectors for now