Merge pull request #7 from nielspetersen/2.7.0

Updated guides for Alchemy v2.7.0
Merge pull request #8 from nielspetersen/2.7.0

Updates the guides chapters
Fixing broken link to "Create Modules" page.
Added missing class keyword.
Changing notice of gem version in Gemfile to ~> v.2.7.1
Adding 'bundle exec' to some shell examples.
Fixing some wordings and sentences.
Moving "what is alchemy" text. Removing old/wrong informations.
Adding PostgreSQL to list of databases
Changing sentences because of the wording.
Update readme
Show correct way of loading authorization file and rendering icon for modules.
fix wrong option name in code example.
Enhancing the example of a picture_gallery element creation.
Add more words for better understanding the alchemy:scaffold task.
Improve element prologue.
Fixes gramar.
Remove sentence that has already been said before and confuses here.
Changes wording
Fix grammar