refactor(game-pane.styl): tweak layout and colors

– Improve positioning and size of chat-box buttons
– Replace some px values with ems
– Replace contributor colors with variables (set in global-colors.styl)
fix(global-modules): prevent labels from hiding tooltips

– Remove overflow:hidden from label template as it obscured tooltips
applied to label’s children
– Style buttons correctly if they include an input element