appDisplay: Only reload frequently used data when mapping the frequent view

If the user mostly uses the All Apps view and uses it as his default view,
we shouldn't reload frequent data after a timeout. Simply do it when the
view is mapped.

https://bugzilla.gnome.org/show_bug.cgi?id=723179
appDisplay: Make AllView handle the display of the all apps view

Rather than having the central component handle it. Just a code tidying-up.

https://bugzilla.gnome.org/show_bug.cgi?id=723179
appDisplay: Make refiltering folders more efficient

Rather than queueing a full redisplay, simply filter the apps inside
folders by toggling the icon's visibility.

https://bugzilla.gnome.org/show_bug.cgi?id=723179
appDisplay: Support the 'categories' key for app folders

https://bugzilla.gnome.org/show_bug.cgi?id=723179
appDisplay: Support the 'excluded-apps' key for app folders

https://bugzilla.gnome.org/show_bug.cgi?id=723179