Fixed checkbox and option group caption wrapping

When an explicit width is set for a CheckBox or OptionGroup on the
server side, the captions will wrap
Added new fonts to choose + lots of small fixes

Roboto, Lato and Lora are now available automatically if you use them
in $v-font-family

Removed many placeholder selectors (not supported by Vaadin Sass
compiler yet, maybe add back later)

Added an optional “common stylenames” import for easy-to-use style
names. Included by default
Switched default font back to Open Sans
Improved inline-icon support

Now you can have a caption text at the same time as an inline icon in a
TextField. TextArea support is still lacking.
Added read-only TextArea styles
Merge branch 'master' of https://github.com/jounik/Valo