change all "ConfigurationSource" in the nice the nicerr "ConfigSource"
remove Role::ConfigSource: useless "optim" that complicated things too much
Mistress.pm: add doc for {forge,remove}_component()
Mistress::App::Command: use new Mistress component API + emphasize YAML
M::Env::Config: missing "require Mistress" made ->_reload_configuration fail
(pretend to) add tests for M::Env::Fs::Disk