Whitespace :scissors:
Add Refinery::Pages::MenuPresenter guide.
Merge pull request #2321 from refinery/menu_presenter_guide

Add Refinery::Pages::MenuPresenter guide.

[ci skip]
Trial less hacks in the CI process for a while.
Extracted complex logic into more readable methods.
Add MenuPresenter specs.
Added suggestion and command to use homebrew for imagemagick install on OSX
Refactored much of extension generation to make it easier to read and adhere to DRY better.
refinerycms-i18n dependency isn't optional anymore.
Due to Capybara upgrade rename reqesuts folder to features.
Add missing files which need to be checked for existence in engine generator specs.
Use String#gsub because it replaces all instances.
Simplify Gemfile for generated engines.

If the user wants to add spec watchers/notifiers then let him do this
job himself.
No longer provide a Guardfile when generating engines.
Specify 2.1.0 for refinerycms-i18n.
Remove the .dev from version.
Add 2.0.x -> 2.1.x upgrade guide and reorder other guides located in the same folder.
Merge pull request #2326 from refinery/upgrade_guide

Add 2.0.x -> 2.1.x upgrade guide and reorder other guides located in the same folder.

[ci skip]
Merge pull request #2319 from refinery/menu_presenter_specs

Add MenuPresenter specs.
Remove notifier gems.

If the user wants to or needs additional gems like notifiers, runners
etc - add them to .gemfile.