Offline building the MoCap app not possible

[OpenUAS]

The CMakefile is made in such a way building cannot be performed offline. This is unhandy when switching branches and connected to a e.g. Bebop over WiFi and the LAN is just the NatNetData. All things Git, one of the main git fetch --all advantages is one can go into the wild and continue development. The issue should be fixed in such a way offline compiling of UnifiedMocapRouter does not halts halfway. Feel free to re-assign the issue.

[tblaha]

That's a fair point. We cannot build UnifiedMocapRouter from scratch if there is no internet, because we have to pull in the natnet sdk binary, and we depend on some git repos.

• git repo's: let's add them as submodules!
• natnet sdk: adding a binary file to the repo doesn't sound like a great idea, but we let CMake check if the file already exists and has good checksum, and only if that's not the case, try to pull it from the web? that way you only need internet the first time you build, or when you clean the build filter. Would that be acceptable? Or would you rather add the binary to this repo?