Refactor Namespaces + Autoloader, Move Many Files

[dac514]

When Namespaces were first introduced in PB back in 2012 we had to fudge a way to make a compromise between our existing legacy code already in place + WP file naming conventions.

Looking at the PB code today we no longer have any code that isn't namespaced yet we are still far from the standards:

• http://www.php-fig.org/psr/psr-0/
• http://www.php-fig.org/psr/psr-4/

Our code should be refactored to better follow the PSR recommendations. Our current Autloader looks for \Pressbooks files in multiple places. This is not standard. Files should be changed & moved so that loading is unambiguous.

For example, according to the PSR (minus the file naming which is a WP standard that conflicts with the PSR standard, but what are you gonna do?) the class \PressBooks\Network_Managers_List_Table should be in /includes/class-pb-network-managers-list-table.php It is not. It is currently In /admin/class-pb-network-managers-list-table.php

In the refactoring effort proposed by this ticket, this Class would be changed to \PressBooks\Admin\Network_Managers_List_Table and the file would be located in /includes/admin/class-pb-network-managers-list-table.php

[dac514]

PS: It is implied by this ticket that /shortcodes/ would be moved to /includes/shortcodes/ and so on.