fix node parameter handling:

comment-parameter only for comment nodes, most parameters not for nodespace, fixed form field visibility accordingly
clone_nodes method for backend (+tests)
add ability to clone to new nodespace
adjust tests.

since the resultset is not sorted anymore, we need to be agnostic of the order of the returned nodes
frontend copy/paste

cmd / ctrl + c and cmd/ctrl + v trigger copy and paste of nodes.
a dialog will ask how it should handle the links.
some mising semicolons
allow to specify offset when pasting nodes
change frontend behaviour. copy/paste via menu
add "delete nodes" to context menu

plus, some cleanup
use topmost, leftmost coordinates for c/p offset

this avoids pasting to negative values
fix copy/paste offset
select pasted nodes after pasting
don't allow copy/paste across nodenets

this is not yet supported
fix delete nodes
enforce disabled
Merge pull request #42 from Doik/copypaste

Merging Copy & Paste, closing TOL-50