Flatten AND queries into single arrays where possible

[jbmorley]

Right now, chaining the && operator, will generate a left-heavy tree of and operations. This has the side effect of generating very unpleasant SQL output, and making it incredibly difficult to represent the conditions in the UI (something like Smart Folder editors throughout macOS). It should be relatively easy to change the implementation to instead model a series of && operations as an array which is much better suited to a list-based editor.

[jbmorley]

This is really only required when we add support for saved searches as it potentially simplifies the UI for the search.