exit after EULA rejection, don't halt

This is less disruptive for people who are just curious to see what
happens if they reject the EULA before actually accepting it.  It
also removes the questionable dependency on sudo and sudoers.
boxes are now on vagrantcloud
tweak download wording
add link to demos
tweak box size
split off manual barclamp proposal instructions into separate page
mention /dev/vdc in manual guide
fix header levels
mention use of VM consoles
Vagrant 1.7.0 ditched VirtualBox as the static default provider

It does automatic detection.
explain how to get admin node up
improve Windows guide
no need to expose URL in text
fix issues running on MacOS X
warn about older VirtualBox 4.3.x
improve HA demo docs on failover and recovery
boxes are now on vagrantcloud!
don't need box building info on "homepage"
add link to Paris workshop
improve grammar