Confirmation for logging out

* New confirmation function
* Made interface functions accessible through window.Interface
Optimize logout confirmation

Re-use window instead of creating a new one each time
Fix Dwarf Fortress launching on Linux.

The launching is still not without problems (the standard streams get muddled
with dfterm3 standard streams) but the Dwarf Fortress does not freeze.

This commit also consolidates Windows and Linux launching to the same module.
Remove useless admin.html. It was not being used at all.
Merge branch 'ui' of git://github.com/lethosor/dfterm3
Fix unintuitive command line option behaviour. (GitHub issue #2)