Trend Arrow and Mobile Alarm fixes

My goals with the pull request are ~~pretty big, so this may take some time...~~ have changed so that a reduced scope can be made available sooner

  - [x] port over all fixes from [my fork](https://github.com/jasoncalabrese/cgm-remote-monitor)
  - [x] add support for trend arrows if available
  - [x] UI to enable audio alarm on mobile browsers