Rename Verification cases to use 'verification' rather than 'validation'

[simopier]

The current documentation and file names list verification cases as validation cases. This PR changes that for relevant cases.

This PR therefore does not add any new feature/V&V cases, only renames existing cases and updates the documentation. (Ref. #12)

[simopier]

@singhgp4321 this is the PR we had talked about to call verification cases what they are rather than validation cases.

[moosebuild]

Job Documentation on 94af93a wanted to post the following:

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[cticenhour]

@simopier I approve this, but since you requested review from @singhgp4321 I will leave it to him to merge in case he has any comments.

[singhgp4321]

Looks good to me.