Changes in backend.

- when requesting a transform a timestamp can now be provided
- user inits are generated directly after class initials and ros
parameters
Several extensions and fixes.

- Package can now be saved with 'ctrl+s' in focused editor.
- Tf listener auxiliary method now prints a warning on exception.
- User inits are generated before pubs/subs/etc now.
- RoslaunchNodeItem has 'args' child now.