aiohttp connection pooling

[UTXOnly]

• Changed query constructor to use AND when adding query clauses, Array searches within id, pubkey, kinds and tags still use OR
  • No longer returning unnecessary rows and bogging down services
  • Resolves #33
• Created WebSocketHandler class to define a single aiohttp.ClientSession object and pool http connections
• Switched order of branches of format_response() to make EVENT type first branch