Add Guava

For @VisibleForTesting
Add README
Minor README tweaks
Minor README tweaks
Minor README tweaks
Minor README tweaks
Minor README tweaks
Add file with IDE configuration
Add link to IDE.md in README.md
Add sample email sending test
Bump project version
Fix package for mutation testing
Make DB connection URL more generic

It should fix problem with incompatibility on Windows and Mac OS.
add tests for the flow in PaymentServlet
Merge branch 'master' into solutions/md5_signature_bug