Old connection data should be cleared

[capeterson]

The max salesforce session timeout is 12 hours - it makes no sense to keep inactives connections cached longer than this. While it's possible they might be valid it ends up as something of a memory leak if you access large numbers of orgs.

Proposal: include a last used timestamp on each connection and if it's >4 hrs (subject to configuration). They will be re-initialized on next use anyways, so the only penalty to this is a few extra API calls if the session was still valid.

[capeterson]

Added config and background job in latest push.