[CHORE] Update to support Spree 2.2-stable

Status
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**READY**


Description
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Updates all portions of the gem required for compatability with Spree 2.2.


Purpose
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- [x] Change references to `AVAILABLE_REPORTS`
- [x] Update layouts/styling on reports pages
- [x] Clean up `README`
- [x] Bump version


Deploy Notes
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Deploy as normal.