Add an icon for feedback in sidenav

[earth2marsh]

In order to move the current feedback button out of the default place where it is and into the consistent sidenav, we need an iconic representation of "send feedback". Recommend styling it after Chet's electric megaphone in the San Jose office.

[ichung1]

Megaphone has been created in 22pt (14pt as well just in case). Sketch file has been updated.

Marking done.

[brandonscript]

We had a good laugh but I don’t think we can ship it like this -- let's have two of the non-"special" versions of this one too just to be safe ;)

[ichung1]

No problem at all. I saved the "special" ones in the sketch file and labeled them as such. The originals are in there as well.