Avoid modulo bias in Random::randomUInt().
Support custom backends in Random.

Useful for tests.
Add tests for Random::randomUInt() and randomUIntRange().
Use QUINT32_MAX in tests instead of hardcoding the number.
Merge branch 'modulo-bias'

https://github.com/keepassx/keepassx/pull/21
Coding style fixes.
Merge remote-tracking branch: upstream/master