fix(ngPluralize): Use "other" pluralization key as a fallback

[Sija]

With languages having optional keys like few or many it's handy to use other as a fallback instead of defining all of the translation keys (in which some may be repeated) in when attribute of ng-pluralize.

Refs #7774

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[Sija]

I've signed the CLA from my gmail address.

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CLAs look good, thanks!

[Sija]

As agreed in #7774 better solution is needed, thus I'm closing this PR.