Implement first parts of file data cacheing and support for flagging files as seen automatically when watched.
Add a custom error handler that logs errors for later examination.
Convert timestamps into numbers when loaded from cache.
Log errors when the cache can't be renamed into place properly.
Remove cache before renaming new one into place to work around weird bug on windows. NOT SAFE. DO NOT KEEP.
Ignore all events when unfocused
Add "toggle seen" command
Add "toggle seen recursive" command