Extract send fees into a page and add scenarios

[GBKS]

Picking up work that Steyn did around various fee scenarios, and tried to marry it with what we have in the guide already. The "Send" page had a lot of fee-related info, but adding more there would have resulted in a very long page. That's why I extracted the fee content into a dedicated page that lives underneath the "Send" page. The "Send" page now only has a very short paragraph about fees and links out to this new page.

Some content changes:

• Tweaked explainers on how fees work, trying to make them more clear
• Added details and visuals for "receiver pays for fee", "custom fee" and "low balance" scenarios
• Tweaked other screens and copy for consistency

🧑🏻‍🏭Check the preview👨🏼‍🏭

Closes #997

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[GBKS]

Thank you for your feedback, dear reviewers. I accepted it all, please take another look and leave your verdict.

[mouxdesign]

Looks good to 🚀