Added "open_all_entries" boolean attribute and database column to the User model.

This boolean (false by default) will control whether all entries are shown as open (if true) or closed (if false) when they are loaded in the read view.
Added checkbox to the edit registration view, to set the value of the open_all_entries attribute of the current user.
The value for the open_all_entries attribute of the current user is retrieved via AJAX when loading the read view.

Pending: make entries open by default if open_all_entries=true. In this case the open_entry variable will not be used; change all uses of this variable accordingly.
Changed checkboxes markup so that they are properly displayed in Chrome.

Before this, they were correctly displayed in Firefox but invisible in Chromium, perhaps other browsers. I'm not very happy with the generated markup and the CSS I have to use to make it look passable, but it looks fine to a normal user.