Make The "Annet" Category Stricter and Improve Contrast

[AdrianAndersen]

Related to mathiazom/rezervo-web#138

The colors are updated to make a better contrast with the ClassPopularityMeter. I think the pinkish color for cardio classes makes more sense than the green one, as it is now more similar to both spinning and dance classes in terms of color. In my head, it makes sense that similar sort of classes (in terms of cardio vs strength) has some level of similar gradients.

Feel free to adjust colors at your leisure, but make sure to get good contrast with the PopularityMeter ✌🏻

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[mathiazom]

Does not sufficiently address mathiazom/rezervo-web#120, so reopening