Issue/724 normalise buttons

[pstenstrm]

All buttons are now styled with the .button class, it has the variations .primary, .secondary and .small.

Previously there were two distinct css "patterns" in use. The global .btn that could be used anywhere, . And four button mixins that were used to style specific elements.

I've opted to remove the mixins and use the former modular pattern for buttons. Since buttons are such a common element removing the use of mixins reduces the overall compiled css filesize by 9.75%.

Closes #724

[buren]

@pstenstrm 🙇

💯 x ❤️ Thank you!

Awesome to both reduce the file size by almost 10% AND also remove potential confusion for new and existing contributors.

I've deployed this to https://just-match-frontend-sta-pr-731.herokuapp.com, so its easy to test without a local version.

Will try to walkthrough this ASAP, so we can merge this.

[buren]

@pstenstrm after a quick check the only issue I could find was the login and forgot password buttons (see screenshots).

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The rest looks great! 👍

[buren]

@pstenstrm 8ea2cf4 did the trick! 👍 Merging.