Change capability required to manage book info, export, and sell books

Book Info requiring only edit_posts seems overly broad (allows default author role access -- authors in WP are low level users) Suggesting edit_theme_options instead. edit_others_posts would be in-between (i.e. default Editor role would have access).

WP Has a native capability called 'export'. Makes sense to use that vs. edit_posts for the PB Export menu so role manager plugins can be used to enable/disable that per role.

Book Sale URLs seem more like options to me so I'd recommend using edit_theme_options (or a custom capability) -- is there a reason it was set to edit_posts? Seems overly broad to me. edit_theme_options seems to make more sense...? This means by default only admins could edit these, but it can be granted to other roles without opening up all options.