Adds AssetHelper library to only compile assets on first run / upgrade. Closes #6
Corrected typo in juju_log
Made errbit charm description more concise and reflects the content of the Discourse charm
Removed nginx service restart line, and port modifications from Start hook, made errbit starting without error mandatory - should fail the node if the servie does not come up.
Strips port close action from Stop hook
re-adds the port opening logic to installation hook