Add action bar with link to raw data to all charts

[pluehne]

This adds an action bar to every chart with a button to download the raw data files in TSV format if existent. The action bar is designed to hold more actions in the future, most notably, a switch for the level of detail in the charts.

Along with the action bar, this commit introduces CSS for buttons.

Note that the action bar is to be considered as a “version 1” design to bring the functionality first, and the layout will probably change in a future release.

For reference, here is a screenshot with the new action bar highlighted:

[filmaj]

Looks great... except on the Collaboration chart page, there is a big gap between the sidebars:

Happens on both a recent Chrome and Firefox (desktop) version. Looks like it might be caused by the col-aside element in each row being vertically-aligned in the middle?

EDIT: I think it is because the collaboration chart is the only chart that uses the row-centered class, which aligns its items in the middle vertically. Changing the class to just row seems to fix this.

[pluehne]

Admittedly, this was intentional. I first put the action bar into the same col-aside as the other info boxes. However, this required some inelegant code (the action bar would have to be inserted directly before the first existing info box, but then it’s difficult to deal with charts that have no info boxes with descriptive texts).

The second reason for leaving the design like this is that I plan to implement a overhaul of the general layout. We’re starting to get to a stage where we have lots of UI elements that clutter the screen, and where it isn’t easy to quickly grasp what controls/elements belong to which group. That’s why I consider the action bar a “version 1” design (as described above) whose main intent is to bring the functionality.

@filmaj, @larsxschneider: Does that make sense to you? If not, I’m definitely open to adjust the layout for the time being.

[filmaj]

Sounds fine to me, certainly not a blocker 👍

[larsxschneider]

Looks good. #87 is minor nit that can be addressed in a separate PR.