Refactor ClientManager

[sarahsnow1]

Overview

Fixes a bug in which cached data in LostClientManager prevented initial locations from being sent to listeners which had been removed and re-added.

Proposed Changes

• Removes ReportedChanges class and simplifies LostClientManager to update information related to last reported location inline rather than use a transactional style API (void updateReportedValues(ReportedChanges changes))
• Simplifies ClientManager API (removes internal state which makes shutdown unnecessary)
• Adds LocationRequestReport to allow simplification of LostClientManager internal state (keeps track of last reported location for given LocationRequest and listener)
• Updates FusionEngine to use recommended Location#getElapsedRealtimeNanos instead of non monotonic Location#getTime
• Updates Clock interface to use nanos rather than millis
• Adds HandlerFactory interface to allow constructor injection and easy mocking in tests
• Updates and adds test coverage
• Updates to gradle plugin 2.3.3

Closes #241

[tallytalwar]

Looks good to me.

Thanks @sarahlensing for explaining the context and issue this was solving offline! 👍

[skypal]

Unfortunately this commit broke the way GPX files are processed:
in LostClientManager.iterateAndNotify(), the timing of locations is eventually compared against location.getElapsedRealtimeNanos(). (Via SystemClock.getElapsedTimeInNanos()
However in TraceThread.nodeToLocation(), there is only a call to location.setTime() but not to location.setElapsedRealtimeNanos()

I created a new issue (#265) that addresses this problem in order to provide a fix as pull request...