[Data Object Editor] Path property in link type

[markus-moser]

Similar to #671

We need the path (or fullPath) property also in the link data type. This is especially relevant when we have the linktype "internal" - so when we link to an Pimcore element. For the link type "direct" we could also fill up this property with the path from the "direct" property (but would also be ok if you leave it as null in that case).

[mattamon]

@markus-moser but this also means that we need to resolves the element first to get the fullpath correct?

[markus-moser]

@mattamon Yes, that's correct!