merge all installation docs to 3.5

Minor tweaks to all docs; added Feedback page to installation docs
(cherry picked from commit dd8938b946d42d4765e042a5ed36baa4186af17f)

Conflicts:
	getting-started/installation.markdown
	getting-started/installation/installation-community.markdown
	getting-started/installation/installation-enterprise-free.markdown
	getting-started/installation/installation-enterprise-vagrant.markdown