[SSHD-553] Make sure all code can be compiled using JDK 7

Highlights:

- Fixed downloading of animal-sniffer-plugin Java 7 signatures
- Fixed bug in passed options during monitored authorized keys re-load
- Display more information if assertions fail for AuthorizedKeysAuthenticatorTest#testAutomaticReload
- Avoid randomization in AuthorizedKeysAuthenticatorTest
- Replaced Files.newBufferedWriter call with JDK-7 compatible calls
- Fix headers check style validation broken by the spaces in the copyright notification
587 files changed