SDM backend and controller / frontend can get out of sync if system packages are updated

[confluence]

If a user upgrades the system packages on a server with an SDM CARTA installed, they may get an updated backend package, but no updated controller or frontend (because those are not installed through system packages). This is more likely to affect users of the -beta packages, and only if we release a new version unexpectedly.

I think that the best way to resolve this is to create a dummy system package which depends on npm and runs the npm install command when it is installed. Each version of this dummy package should install a specific hardcoded controller package version, so that older packages can be used to downgrade. The user would install this package when setting up CARTA instead of running the npm command manually, and once it is installed it will be upgraded whenever all the packages are upgraded.

I will investigate how to do this on Ubuntu -- some care may be required to make sure that the package can install and uninstall itself cleanly. If this is successful, we should probably implement something similar for the RedHat / CentOS packages.

[confluence]

After discussion with @veggiesaurus, we think that it would be simpler to display a warning in the frontend if the backend and frontend versions don't match -- only a warning, in case someone is deliberately mixing and matching. I'm reassigning this. :)