Igcs 55 telemetry loggers

Basic binary telemetry logging support (The rlog CSV format is not supported yet)

- Create a new log file each time we begin receiving data after the app has launched
- Log file is created in the apps document directory and can be accessed via the Xcode
  organizer for now.
- We can create log files in the format yyyy-MM-dd-HHmmss in either UTC or the apps
  default timezone. For now log files are in UTC.
- The following utility classes have been added to the project: FileUtils and DateTimeUtils

Open questions for this review:
- I'm not sure either the systemTimeInMicroseconds or the unixTimeInMicroseconds method in 
  DateTimeUtils is correct.
- Right now each mavlink msg is written to the open log file via a background queue, this may or may not
  really be needed. In addition each message is put on the background queue individually instead of 
  accumulating them into a larger buffer. This could also be sub optimal. Let me know your thoughts either in the PR or offline.
- Line 56 in CommController still needs un-commened in order to test with our bluetooth setup. I have not tested with redpark cable yet.