Moved checksum's and download url calculation into helper.rb

[katbyte]

This allows calling cookbooks to change the version on the fly.

Followed the pattern in:

• https://github.com/parallels-cookbooks/confluence
• https://github.com/bflad/chef-jira
• https://github.com/afklm/crowd

Issue #167

[katbyte]

@linc01n I noticed you merged the versions PR. Rebased this off that branch so there would be no merge conflict. If you accept this one i also have the newest version checksums added and can create a PR for them aswell:

https://github.com/katbyte/chef-stash/tree/versions.201610

[iluxame]

@katbyte we also waiting for this PR. Do you intend to fix coding style stuff in order to pass CI?

[katbyte]

@iluxame I have rebased this PR off the latest master, however the errors causing the CI build to fail do not seem related to my changes (but i could be wrong)

@linc01n Is there a reason this PR was not merged? Is there anything I can improve/fix?

[linc01n]

Sorry for the late reply.
What I am concerned is moving this out of the attribute.rb is that the right way to do.
I asked this question to some chef people when I was attending a workshop. He said it should be fine.

Going to merge this PR now.

Thanks!

[linc01n]

Fixed the rubocop and foodcritic error. Changed the helper a bit in #182