TourDino has global styles

[keckelt]

Hi!

I noticed some side effects from TourDino's css in Coral.

As the name suggests, the _global.scss has some styles that are not scoped by any TourDino container element.
While most of them are for TourDino specific css classes, there is a general button style that cause issues as it aplies to any button with an img inside (as an icon): https://github.com/Caleydo/tourdino/blob/master/src/scss/base/_global.scss#L94-L105

Do you agree with me that this should be fixed?