Use Secure RNG to gather entropy #83

Currently on Android (and other platforms as well, TBC) the following message is shown at start up:

I/System.out: Not enough entropy available.
    Trying to gather entropy (randomness) by reading the disk...
    You should consider installing a better random number generator e.g. haveged.

Describe the solution you'd like
A Secure RNG should be used to generate entropy. On Android: https://developer.android.com/reference/java/security/SecureRandom

Additional context
By gathering entropy from the disk the startup can take various minutes depending on the Device.