Implementing PLUSHU_APP_NAME

[stuartpb]

Changes need to be made in:

• [x] plushu/plushu-apps
• [x] plushu/plushu-config
• [x] plushu/plushu-domains
• [ ] plushu/plushu-dokku (commands)
• [ ] plushu/plushu-addons
• [x] plushu/plushu-logs

and will need to be carried through for any future plugins that take app specifications.

The pattern is something like this:

if [[ -n "$PLUSHU_APP_NAME" ]]; then
  app=$PLUSHU_APP_NAME
elif [[ -n "$2" ]]; then
  app=$2
  shift
else
  echo "Missing app name" >&2
  exit 1
fi

and further arguments are defined from $2 on.

Once this is integrated into the correct plugins, it should be added to:

• [x] plushu/plushu-plusku
• [x] plushu/plushu-dokku
• [x] plushu/pluchu

[stuartpb]

Renamed the variable to match PLUSHU_REPO_NAME etc.

[stuartpb]

The commands in plushu-dokku and all of plushu_addons aren't really written yet, so this is pretty much ready to move forward.