change navString to emit ISO 8601 date string of date that is >50% in view
change 'navigated' to emit array because two-week will have to emit array
change navString to array of two ISO 8601 strings representing the two-week view endpoints
replace '12 am' tick labels with 'Jan 1'-style dates
Merge branch 'master' into jebeck/one-day-navstring
bugfix: was emitting wrong beginning endpoint for two-week view
put back transform to lowercase in two-week view day labels
Merge pull request #49 from tidepool-org/jebeck/one-day-navstring

improve format of dates in tideline navbar