Issue here is that for some reason click in tree causes 2 events:
- Selection Changed
- Resource Opened
Due to this, we get the markdown event 2 times and this misbehaves.
I am not confident in changing markdown so implemented similar pattern:
- Throttle requests if they're for the same resource inside 300ms
- This means 2nd event is ignored
Testing:
- Manual, clicked a bunch of markdowns
- It "just works" for me now
* added previous and next buttons
* previous and next notebook API
* links for prev/next notebooks
* fixed first and last pages
* made code more readable
* addressed Kevin's comments
* moved logic over to BookTreeItem
* show buttons in dev mode only
* added BookTreeItemFormat interface
* added interface and enum
* removed localize call
