Add new updating tool to remove some of the tedium

This is an automation tool I wrote so the updating process could be slightly less tedious and very much less user-error-prone. I've been using it for a short while, and it behaves quite robustly (at least for the normal use-case as I understand it), so I tidied it up and added `--help`, etc for it to be more user-friendly. It is in strict POSIX shell so should be at least as portable as IXP-Manager (unless I missed something). I kept the code as clean as possible so it should be self-explanatory enough when reading it with a half-decent syntax-highlighter. I have deliberately left the "update-schemas" part unimplemented and shell out for it to be done manually, because the "quick way" to do it is not the "best way", and it is better to wait and do it the better way (using the Doctrine output, as mentioned in this script's comments). If you wish to leave it undocumented, I will understand ;-) Of course if you do wish to refer to it in documentation be sure to warn people about what I say in the comments just for the sake of prudence (always do a dry-run first, even then do a backup of files and DB before running it for real).