Remove left/right page choices in UI
Context
Given discussion on #615 (closed), we should remove the left/right start page choice in the Ketida UI across the instances, and revisit during in a Ketida redesign later this year.
During redesign we will consider output-specific page refinement at the export stage, rather than a global choice per component in the book manager.
Proposal
Remove the left/right page markers in the book manager UI. Exports will use the start page default of the chosen template.