Investigate adding a refresh lock

[sea-kelp]

Currently, the refresh is triggered by visiting the site. If someone visits the site while it's updating, it's possible for a second refresh to be kicked off without respecting the refresh interval. This can lead to duplicate updates being posted which can be confusing. An additional question I'm curious about is whether there would be any issues implementing the lock in the db when there are multiple threads/processes accessing the same sqlite file