Various tweaks for devenv

Created by: slifty

While working on the development environment I've made a few minor improvements, focused on the 100Change2020 competition. This PR adds those, although it does not systematize them across other competitions.

Key highlights:

1. Some typo fixes
2. Adding php-mysql as a dependency for the mediawiki task
3. Support for a -g flag, accepting a gpg passphrase, to the 100Change2020 deploy script.
4. A small tweak to prevent (breakingly) empty simplesaml configuration values.