Collapse long quoted blocks within the email body

[mikegioia]

Plaintext emails contain lots of quotes, often multiply nested:

> asd
>> asd asd
>> asdasd aksdj al
>>> akjsdh akjsdh a
>>> akjsdh akjsd
>> askjdh
> asda

This should be collapsed into a group that can be expanded. Might want to start from the bottom and handle it that way until a non-quoted line is hit.