Quiver timeline, diachronic view - add legend for color coding

[MareenGeestmann]

Add legend for color coding.
What does a "green", "yellow", and "red" line mean?

green: better
yellow: equal
red: worse
... in comparison to last release.

In fact, it differs between metrics. E. g. for "Pages per minutes" higher values are better while for "CER Mean" lower values are better.
Hence, the legend must fit the metric.

See also: #42

[MareenGeestmann]

Does "positive", "neutral", "negative" refer to the slope?
Why not better, equal, worse?

[paulpestov]

Fixed

[MareenGeestmann]

I do not understand the coloring - in some cases it is green when values are lower, in other cases when values are larger (within the same metric, e. g. pages per minute).

[paulpestov]

Does it belong to this issue? Maybe you could open a new issue with some examples?

[MareenGeestmann]

Correct, it does not refer to the legend.