Move to open sans font

To follow patternfly/rcue - move over to using primarily Open Sans fonts for headers, paragraph text, labels, etc.

https://www.patternfly.org/visual-styles/

This font is more nicely spaced than Helvetica-Neue which will make some of the text easier to read as well.

May need to consider which text areas should use "light" vs "regular" vs "semi-bold" vs "bold" as part of this change-over.