Replaced Museo font

As per Issue #101 and the licensing conflict with the Museo font- I've created a variation of the Fauna One font that more closely resembles Museo. This font is being released by Mailpile project under the SIL Open Font License (OFL) so is now legal with Mailpile's license for redistribution. 

Currently this font still needs a bit of improvement and additional weights created, but it's start!