Wafer 0.7.6

A bug-fix release for wafer 0.7

• Fix a bug where non-Latin1 titles would crash the slug parsing code
• Fix the incorrect display of css classes in the schedule admin page
• Make more of the model descriptions and help text transaltable
• Separate the display of multiple speakers on the talk page
• When editing an existing talk, use "Save" rather than "Submit"
• Test with python 3.7 on travis
• Add a "highlight-venue" parameter to add a css styling hook to schedule items in a specific venue
• Add a few more tests