Logging framework

[iluwatar]

Instead of printing output to System.out we should use a logging framework such as Log4j to allow redirecting and filtering of output. In some cases this also eases testing. The refactoring should be applied across all the patterns.

[dbryla]

I'll handle this. :) I propose to go with SLF4J API and Logback implementation.

[iluwatar]

@dbryla the proposal is ok for me, you are good to go.

[dbryla]

Should I leave System.out in applications with tests based on StdOut or should I rewrite tests?

[iluwatar]

We want to migrate the tests also. If it causes trouble we can deal with it later.

[dbryla]

PR: #515

Build on travis failed:

The log length has exceeded the limit of 4 Megabytes (this usually means that test suite is raising the same exception over and over).

The build has been terminated.

Can we increase limit?