Allow a limit to be passed to file::read_utf8

Currently the API does not allow the caller to know that the data was actually truncated.
Limit QuickLook preview to the first 20 KiB of the file

This was suggested in pull request #1226. Ideally we would make the limit flexible, e.g. see how much we can generate in 1-2 seconds, but that is a non-trivial change, so the fixed limit will do for now, and while truncated data is suboptimal, it’s better than being killed due to QL manager’s timeout.
Reference MGScopeBar class to prevent linker from stripping it

We instantiate the class in the xib file, so the linker does not know that we actually need it.

Currently the filter list framework use MGScopeBar, which is why this issue is not an actual problem (yet).
Implement intrinsicContentSize for OakKeyEquivalentView

This will allow it to be used with constraint based layouts.
Make OakChooser’s cancel: method public API
Let the bundle item chooser inherit from OakChooser
Remove old filter list code
Move files on disk
Only set search field as first responder if it’s in the window

For example the bundle item chooser may swap it out with a key equivalent view.
Ensure we “search by title” when opening the bundle item chooser