filemanager: use pre-compiled binaries

[mmalenic]

In order to speed up build times, it might be useful to pre-compile the filemanager binary and use that instead of building each time.

The filemanager would still be need to be re-compiled when changed, but I think that separating the compilation from the parts of the build process that test or use filemanager would speed things up because those components wouldn't need to compile their own version of filemanager. E.g. this could be useful for the integration tests that are part of the FMAnnotator, or just for speeding up the stateless tests in general.