Quote button: add angle bracket at beginning of each newline

Hey all! Thanks for all the hard work! This is my first issue on the Gitter project ;)

Currently, when using this button, it adds a single square bracket before the message. In simple plaintext situations (ie. when detecting no complex blocks, tables, etc.) it would be great if it quoted the whole message.

It seems that the formatting is forgiving, and so quotes could be added for each newline:

> this is a paragraph
>
> and another

Or for only the start of paragraphs:

> this is a paragraph

> and another

Perhaps the first option wold be best though, in case Gitter wanted to start following the markdown spec more closely in the future :)

Anyhow, thanks for any consideration you might give this! Y'all are awesome

Screenshot

Screen_Shot_2018-11-06_at_7.06.59_PM

Relevant code

Edited by Eric Eastwood