Add new features to BLE_EddystoneService

[andresag01]

The following features were added:

• It is now possible to stop any BLE activity from the Eddystone library. See EddystoneService::stopCurrentService().
• Added yotta config options to easily modify the default values for the following:
  • URL
  • URL frame interval
  • UID frame interval
  • TLM frame interval
  • BLE Device Name
  • Eddystone-URL configuration service advertising interval
• Refactor the PersistantStorageHelper to easily allow other platform-specific implementations to be added.

NOTE: Some of these changes still need to be tested!

@pan- @jaustin @janjongboom

[janjongboom]

See #57, so we don't have to push to @andresag01's remote.