Suggestion: add missing styles to new `dorothy-warnings` system

[balupton]

Currently a missing style will only be noted in verbose mode. We should use the new dorothy-warnings system introduced in #254 to raise missing styles such that they can be addressed in a non-invasive way.

[balupton]

relevant lines:

https://github.com/bevry/dorothy/blame/95044080e9a67f78fa10f348eb5f22b827650b2c/config/styles.bash#L773-L776

dorothy/commands/echo-style

Lines 216 to 219 in 9504408

	# only respect found on versions of bash that can detect accurately detect it, as otherwise empty values will be confused as not found
	if [[ $found == 'no' && $IS_BASH_VERSION_OUTDATED == 'no' ]]; then
	MISSING_STYLES+=("${style}")
	fi