Fix hearbeats

[Cykooz]

• Fixed processing of heartbeats and a session expiration.
• Fixed ping-pong based heartbeats for web-socket connections.
• Added arguments heartbeat_delay and disconnect_delay into Session.__init__().
• Added argument disconnect_delay into SessionManager.__init__().
• Breaking change: Removed argument timeout from Session.__init__() and SessionManager.__init__().
• Breaking change: Argument heartbeat of SessionManager.__init__() renamed into heartbeat_delay.
• Breaking change: Session.registry renamed into Session.app.
• Breaking change: Deleted method SessionManager.route_url().
• Breaking change: Dropped support of Python < 3.7

[lgtm-com[bot]]

This pull request introduces 1 alert and fixes 1 when merging 2b89b0e3035e6d5e191897aab40698c18bb1e52c into 74042149507d967edca42b2f444594df4939ddc0 - view on LGTM.com

new alerts:

• 1 for Module is imported with 'import' and 'import from'

fixed alerts:

• 1 for Module is imported with 'import' and 'import from'

[Cykooz]

Hmm... Travis CI don't work