#27 Several graph algorithms including cycle checks

[gunnarmorling]

Supersedes #31, but only style changes so far:

• No $%§!! Windows line-breaks; also added .gitattributes to ensure line breaks are nomalized in the repo
• Avoiding dependency to Guava
• Formatting

[gunnarmorling]

Hey @wuetherich and @nilshartmann, it's still work in progress, but some first success with hooking up the cycle detection algorithm with the rest of Deptective:

[gunnarmorling]

I'm going to merge this one. The implementation isn't ideal yet, but it's doing the job well enough. The following behavior has been implemented:

• During VALIDATE mode, any cycles in the architecture model (deptective.json) will cause a build error by default (can be changed to warning via -Adeptective.cycle_reporting_policy). That is because the target model shouldn't contain cycles. Note that any unintended relationships in the actual code that form a cycle will be report as an illegal dependency just as before.
• During ANALYZE mode, any cycles in the actual code base will cause a build warning. The model should be altered to break up the cycle before validating against it.

Thanks a lot for the algorithm implementation, @wuetherich!