fully configurable version mismatch detection

It is hard to fix the dedicated server because it blocks {DEV_VERSION} by default with some obscure hard-coded conditionals. There are also other annoyances:
* People can bomb in with their self-compiled {DEV_VERSION} if the server is not dedicated although we warn in the lobby about that.
* People bomb into @Scott_NZ and mine {DEV_VERSION} test-games with their stable releases and we have to explain them or rudely kick them over and over again.

This addresses everything by introducing two new variables:

1. Reject from connections different versions (also covers the case if people direct connect overriding the server browser GUI based check)
2. Add a new Debug options so you can join every game with every version (if the server allows it, which he does not by default)

Still warn about {DEV_VERSION} as we don't know which commit we are on.

I also decided to ship the launch script from https://github.com/OpenRA/OpenRA/wiki/Dedicated because it has sane defaults. Everyone should use it.