Command to copy the raw apps settings from one engine to another.

To prepare for the release of the desktop application, this pull request adds a new core command to copy the apps settings from one engine to another.  The intended use is to be able to automatically setup the tk-desktop engine for a project with an existing configuration based off of the current tk-shell settings, avoiding the need to initially setup the desktop engine manually.

The new command uses a new method in Environment that copies the raw yml structure that makes up the source apps value to the destination engine.
Saw that line although I wasn't 100% clear on what a "tank command" was.  I could go either way with this.  Seemed like allowing it was easy enough.