Integrate --layout-json command line parameter so that it can be passed to dbus

[mattrose]

From the gitter chat.

The dynamic layout thing worked like a charm, but one issue I'm facing now is that I can't close the terminator shell from which I call the terminator -u -j data/layout-files-examples/2-columns.json without actually killing the newly opened up terminator layout. In older versions, the layouts would run detached from the called terminator shell, so I could always do terminator --layout test-layout && exit. But in the case of dynamic layouts, as long as the newly created layout exists, I can't exit from its parent shell.