closes#12118
- server.start was mistakenly removed in 71f02d25e9
- it is used for loading themes (and other things) and is critical
- added tests to prevent this regressing again in future
- the announce functions exist for the purpose of communicating with Ghost CLI
- the functions were called announceServerStart and announceServerStopped, which implies they tell Ghost CLI when the server starts and stops
- however, the true intention / purpose of these functions is to:
- either tell Ghost CLI when Ghost has successfully booted (e.g. is ready to serve requests)
- or tell Ghost CLI when the server failed to boot, and report the error so that Ghost CLI can communicate it to the user
- therefore, I've refactored the old functions into 1 function to make it clearer they do the same job, but with 2 different states
- also added some tests :D
