make "dart format" check non-scoring check

[jonasfj]

When/if the default line width for dart format becomes configurable, as being discussed in dart-lang/dart_style#833, we should do the following:

• Stop granting point for code being formatted with "dart format".
• Make a suggestion when code is not formatted with "dart format" (but not points deducted).
• Increase point for up-to-date dependencies from 10 to 20 points.
  (Ensuring overall points remain the same).

Reasoning: Code formatting does not imply quality. But we do want to make people aware that formatting is a thing, if they haven't otherwise discovered it.