Add more review rules 446

[frankschmitt]

Enables the remaining Unused review rules as discussed in #446. Things to note:

• a couple of files have been excluded because they're reported, but are essential for the executable to work properly (false positives, see discussion for Add elm review for our elm code #446)
• some minor changes to the copied external modules were necessary to make elm-review happy; if we decide to re-import them in the future, we'll need to re-apply these changes. This is not the optimal solution; we should probably either try to get the upstream modules to also use elm-review and clean up unused imports etc. or exclude them from elm-review.

Suggestions / feedback welcome :-)

[harrysarson]

Thank you!

• some minor changes to the copied external modules were necessary to make elm-review happy; if we decide to re-import them in the future, we'll need to re-apply these changes. This is not the optimal solution; we should probably either try to get the upstream modules to also use elm-review and clean up unused imports etc. or exclude them from elm-review.

Let's worry about this when it is time to update these modules