Persist active storage uploads between deployments

[cattywampus]

Resolves #1

Description

With the introduction of Active Storage in Rails 5, each new deployment was causing the images that have been uploaded to be lost. This fix ensures that uploads managed by Active Storage are persisted and carried along between deployments so logos don't need to be re-uploaded.

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

To test this, deploy a version of the site without using the fix (i.e., without the updated linked_dirs setting in capistrano). This is actually easy to do since capistrano cues off of the code in your working directory rather than in the branch you are trying to deploy.

On the remote server, you'll need to delete the ~/apps/diaper_base/shared/storage folder, since it's existence in combination with the code in the branch fixes the issue.

 # This is so your local capistrano config has the fix
git checkout --track origin/active_storage_prawn  

# this will break the logos by creating a new release, leaving the previously updated
# logos in the previous release directory. But this will also create a new storage folder
# in shared/ and symlink it to the new deployment. Since the is a fresh setup, the logos 
# will be broken.
cap production deploy BRANCH=active_storage_prawn

# go to the test site and re-upload a logo. 

# Deploy a 2nd time and the logo should persist
cap production deploy BRANCH=active_storage_prawn