Port attachment to be an extension

[yorik]

@yorik: To make sketches Attachable Part2DObject has been derived from Attachable Object in the past. A side effect of this was that in Draft objects became attachable, they all have those properties now. With the introduced change we would be able to redo this, e.g. make draft objects not atachable while sketches stay attachable. Is this of interest for you?

Sorry ickby, just saw this now. Honestly I never used the attachment thing with draft objects. It seems much less important, sketches are very often meant to stick on something, while draft stuff is generally used as free-form helper geometry. If anyone needs this, it will now be easy to re-add the functionality I believe, but it doesn't seem necessary to me to do it if nobody needs it.

[DeepSOIC]

I think attachment can be removed from Draft stuff, since we already have it for corresponding Part stuff. Except maybe for ShapeString and Clone.

I have updated Lattice's Attached Placement to work again. However I faced a problem that Attached Placements from earlier projects fail in the new version, because there is no Part::AttachableObjettPython anymore. Same happened to Clones: they just vanish (I don't even see any warning/error messages!).

clone test.FCStd

created in FC rev.<9177, no Clone object when opened in rev. 9422

(3.8 KiB) Downloaded 23 times

OLD:
OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.17.8361 (Git)
Build type: Release
Branch: DeepSOIC10
Hash: 4ac7673e543274bcae856872033a114c7b60481b
Python version: 2.7.8
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.0.0

NEW:
OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.17.9422 (Git)
Build type: Debug
Branch: (HEAD detached at FC/master)
Hash: 6378f611582b47840d771cdc23324a66c67d0e22
Python version: 2.7.8
Qt version: 4.8.7
Coin version: 4.0.0a
OCC version: 7.0.0