Adding a new class for abstracting out application(scheduler). Also moving some initialization code from ble_app_timer.
The class has the only ctor parameter which can be used for configuring the application scheduler. Currently the configuration parameters is used for setting up the scheduler queue and app-timer queue.. The default params are good enough for small projects, for bigger ones they need to be reviewed.

Class BLEApplication is a singleton, i.e. there should be only one instance of it. The instance can be accessed by BLEApplication::instance, and it's the first call creates the static object.

BLEApplication::initialize also starts the RTC timer, so the project doesn't have to instantiate and start softdevice.
Got rid of the application-scheduler related code, BLEApplication is now responsible for that.
Adding the new tester.
Adding the new compilation unit to the library.
Switched to using BLEApplication.
Also greatly simplified the code.