Remove dependency on commons-collections4

[Thomas Zimmermann]

For some general motivation on removing dependencies see #231.

The only used methods are:

• org.apache.commons.collections4.CollectionUtils::is(Not)Empty
• org.apache.commons.collections4.MapUtils::is(Not)Empty

Suggested solution:

• Write own versions or even check inline

[Vladimir Dzhuvinov]

Done: f14097f

[Thomas Zimmermann]

Awesome, thank you! :)

[Vladimir Dzhuvinov]

You're welcome :) If you happen to be coming to the OAuth workshop in Trento next week, or some other related event, let us know, I'm always pleased to meet with users and developers of this project.