Strong params fix for Rails forms

[georgepalmer]

Fix for part of #1287

As a Rails form will include other params such as a commit, utf_8 and authenticity_token we need to pull out only the params we require or we'll get a strong params exception when running Rails with the setting:

config.action_controller.action_on_unpermitted_parameters = :raise

[doorkeeper-bot]

	3 Warnings
⚠️	There’re library changes, but not tests. That’s OK as long as you’re refactoring existing code.
⚠️	Please include a changelog entry. You can find it at CHANGELOG.md.You can skip this warning only if you made some typo fix or other small changes that didn’t affect the API.
⚠️	Please squash all your commits to a single one

Here's an example of a CHANGELOG.md entry:

- [#1297] Strong params fix for rails forms.

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[georgepalmer]

Closing this off for a PR with squashed commits