Prevent the delesion of nodes that are still required by other segments/ways (Checked in V226)

[Ben]

Now that ways all get downloaded in there entirety It is posible to edit them without consideration for what conencts to them. It is posible to delete a node from the way that something may connect to. If you then download that area in full, a way that did conenct there has a segment connecting to nothing.

Ideally it would just be inposible to delete these nodes. but...if that is something that requires a lot of work, for the time being I think the following would be very effective:

Any area outside of the area that can be seen on screen when a download is requested should be shaded grey. This would make it clear when you start editing in an area that you havn't downloaded, but rather just have data running into from the area wich you did download.

Hope that makes sence

Cheers

[imi]

Forbidding the deletion of nodes that are used by other primitives should be done in the server.

the rest is a duplicate of #149