Restructure code and index rollover polling

Notable changes:

• index rollover now run on a polling loop rather than just at startup
• using graceful for controlled http shutdown
• index name now configurable via ES_ALIAS
  • create active write alias as ES_ALIAS
  • create index with name ES_ALIAS and a numbered suffix eg prom-metrics-1
  • create index template with passed settings (shards/replicas/mappings/etc)
  • no need for search alias as now uses wildcard search ie <ES_ALIAS>-*

Breaking changes:

• configuration parameters
• listening address is now :8000