Add explicit typing for 'this' references.

[CNBoland]

Please fill in this template.

• [ x ] Use a meaningful title for the pull request. Include the name of the package modified.
• [ x ] Test the change in your own code. (Compile and run.)
• [ x ] Add or edit tests to reflect the change. (Run with npm test.)
• [ x ] Follow the advice from the readme.
• [ x ] Avoid common mistakes.
• [ x ] Run npm run lint package-name (or tsc if no tslint.json is present).

Select one of these and delete the others:

If changing an existing definition:

• [ x ] Provide a URL to documentation or source code which provides context for the suggested changes:
  <This function types microsoft/TypeScript#6739>
  <https://datatables.net/reference/api/columns().every()>
  <https://datatables.net/reference/api/cells().every()>
  <https://datatables.net/reference/api/columns().every()>
  <https://datatables.net/reference/api/rows().every()>
• [ x ] Increase the version number in the header if appropriate.
• [ x ] If you are making substantial changes, consider adding a tslint.json containing { "extends": "dtslint/dt.json" }.

[typescript-bot]

@CNBoland Thank you for submitting this PR!

🔔 @Silver-Connection @omidkrad @pragmatrix - please review this PR in the next few days. Be sure to explicitly select Approve or Request Changes in the GitHub UI so I know what's going on.

If no reviewer appears after a week, a DefinitelyTyped maintainer will review the PR instead.

[typescript-bot]

Since you're a listed owner and the build passed, this PR is fast-tracked. A maintainer will merge shortly. If it shouldn't be merged yet, please leave a comment saying so and we'll wait. Thank you for your contribution to DefinitelyTyped!

[DanielRosenwasser]

Thanks!