First update in just over a year.

Finally decided to come back to this project and clean a few things up.

To allow data persistence when leaving activity (but while maintaining an active connection):
* New class created to handle session data, "MonitorSession".
* MonitorSession is instantiated by the HeartRateMonitorService (which is invoked with startForeground).
* HeartRateMonitorService updates the data in MonitorSession.

To accommodate future graphing of acquired data:
* New class created to handle timestamped data, "TimestampedArray".

General improvements:
* Improvements made to the main activity UI.
* Decoupled acquired session data from main activity.
* Decoupled ANT+ connectivity from session start (clock button starts session).

Still to do:
* Add in graphing functionality for the HR and Signal data and display other statistics.

Signed-off-by: Adam Thwaites <thwaites.adam@gmail.com>