Check and Repair a version directory

[caesay]

It would be useful for several reasons to allow 'repairing' an install. We can allow applications to repair themselves via UpdateManager, but also allow a "Repair" option via Programs & Features.

• It gives us an opportunity to update to the latest version if a broken app version was shipped and is now bricked from receiving further updates.
• It gives us another opportunity to install any missing runtimes, if an update was performed in error that requires a new framework.
• It allows users to fix mistakes if they were fiddling with the application files and broke something accidentally.

[caesay]

It is no longer relevant to check for missing runtimes when 'repairing', since this is done every time the app starts in current dev branches.

[caesay]

I am going to cover off the rest of this in #70