Find replacement font for Open Sans or resolve its licensing

Problem/Motivation

Open Sans is not GPLv2-compliant and therefore cannot be used as a part of Spark.

Proposed resolution

Possible solutions:

1. Use Source Sans, which out of necessity has already been included in the new release as a temporary or possibly permanent solution.
2. Find a different font that is GPLv2-compliant that is close to Open Sans.
3. See if there is a way to relicense Open Sans so it may be used as the Spark font.