Add burger menu placeholder to DOM
Add menu-area into DOM

While doing that, layouts were converted to use flexboxes instead of
"position: absolute" trickery.
Convert styles to resemble Google material design

First steps, just making it look enough pretty for development purposes.
Tweak text area styles

Whitespace and color prototyping.
Select text colors across document
Add styling to channel list
Add padding between message lines
Add border around message input area
Fix typo in main.less
Remove input field gradient in FF mobile
Channel list in burger menu for small screens