Upon losing access to Strategic Ressources, alert the user if they have any units using that resource

**Issue by [layzsmurf](https://github.com/layzsmurf)**
_Friday Nov 11, 2016 at 07:52 GMT_
_Originally opened as https://github.com/CQUI-Org/cqui/issues/75_

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The default UI does hide this information from the player. E.g. if you lose access to Iron, your Swordman won´t heal, but you still can issue the "rest until healed" command.

One Idea would be to grey out this the rest until heal button - with a mouse over message saying, that its missing resources.

Maybe a message on the right would also be helpful - E.g. damage unit $Name cannot heal due missing strategic ressource $Ressource.

No source file or test is identified. Reproduce the “rest until healed” flow after losing access to Iron, then clarify whether completion means disabling or annotating the command, showing a right-side warning, or both, including the missing resource and affected unit.

Written by the indexing model from the issue text.