Phantom types: Logical paddings and margins

[dzuk-mutant]

These were either not on the checklists or self-assigned by someone else as far as I could see so I figured it would be okay to make a PR request for them ^^ (Reading some more I think someone removed the padding ones because they used to be tagged as experimental, they are no longer considered experimental.)

Adds implementations for:

• padding-block (including 1 and 2-argument variants)
• padding-block-start
• padding-block-end
• padding-inline (including 1 and 2-argument variants)
• padding-inline-start
• padding-inline-end
• margin-block (including 1 and 2-argument variants)
• margin-block-start
• margin-block-end
• margin-inline (including 1 and 2-argument variants)
• margin-inline-start
• margin-inline-end

[dzuk-mutant]

Closing the pull request given the current state of elm-css and the fact that with this branch, I am now planning to do my own fork and have basically revamped the entire file at this point ^^