ability to decide where URLs are opened

[Antoine Martin]

Split from #168 - see there for details.

What we want is the ability for the user connected to the session to decide what to do with requests (within that session) for opening new files and URLs.
Give them 3 options:

• open them as normal (application used will be part of the same session as the one that launched it) - current behaviour
• open them in a new session (create a new session and attach it automatically)
• open them on the client (only valid for URLs, files would have to be copied over first which is a lot more tricky!)

[Antoine Martin]

mostly done in r4472 (+ r4473 for the missing bits..)- see screenshot of the config options

still TODO:

• trap lxde-open too? and kde equivallents?
• transfer remote files to open here (should be tied with remote file browser enhancements to provide "open-on-client" functionality - reverse of what we have now)

[Antoine Martin]

shows the new options for opening urls and files on the server