server-mode: Add infrastructure to watch the filesystem

Enable the server to watch for filesystem changes. This patch includes
* The infrastructure for the file watching
* makes that infrastructure available to cmServerProtocols
* Resets the filesystemwatchers on "configure"
2 jobs for merge/cmake-server-filewatcher
Status Job ID Name Coverage
  External
passed kwrobot-commit-check

passed kwrobot-commit-check