Changed storing of backups to prefixed file

This enables the owner of the bucket to set an expiration policy for
prefix 'backup/' and have backups deleted time X after creation.
Otherwise the backups are cluttering the bucket and have to be cleaned
manually.
Updated framework to access HerokuConfigStore
Added wrapper to access Heroku ENV vars
Added .env file to ignore not to push configuration to github
Merge branch 'feature/herokuconfig'
Added marker for logged in account

This helps users of newer Chrome versions which does not longer show
the URL to determine in which account they are working without much
changes to the UI by just opening the "Switch Account" menu.
Merge branch 'feature/accountmarker'
Prepared release v1.4