New: Added bidirectional CPLevelIndicator behaviour

Depending on whether min < max or max > min CPLevelIndicator changes the order of the normal/warning/critical color. This commit enables this behavior for both cases.
Merge pull request #2071 from krodelin/feature-CPLevelIndicator

New: Added bidirectional CPLevelIndicator behaviour
New: visual test for warning/critical state in CPLevelIndicator.

This change makes sure there is both a level indicator which goes into warning and critical display mode for low levels and one which goes into the same for high levels in the manual test for level indicator.

Refs #2071.
Test: CPLevelIndicatorTest.

Refs #2071.