Option to only show items with selected property

[b-camphart]

From #13 Right now, by default, all notes are pulled into the timeline. If they don't have the selected property, it defaults to a 0 value. This can be useful to prevent a note taker from losing track of their notes, but sometimes, someone may want to only display the notes that actually have the selected property.

Currently, using a filter like [propname] or [propname:propvalue] should filter out items that don't have the property, but this can be annoying to have to update each time the selected property is changed.

Perhaps, instead, there can be a toggle of some form that enables filtering out notes that don't have the selected property. Possibly located under the Filter setting.