Allow users to preview and edit their organisation details

Needed for #184
Preview is an actual preview

Added detailed tests too
Merge branch 'master' of https://github.com/theodi/member-directory into feature-81-preview-and-view-listing

Conflicts:
	app/controllers/organizations_controller.rb
Made tests less brittle
Changed 'Submit' button on the edit page to 'Preview'
Merge pull request #56 from theodi/feature-81-preview-and-view-listing

Allow users to preview and edit their organisation details