Pre 2.0.0

[itthinx]

• Changed the access restriction model to group-based access restrictions.
• Provides an optional legacy mode that supports the previous capability-based access restrictions.
• Optimized the approach to restrict read access on posts using groups rather than access restriction capabilities.
• Added the groups_restrict_access capability which grants users to impose access restrictions.
• Fixed the order_by and order parameters in Groups_Group::get_groups()
• Added the $create parameter in Groups_UIE::render_select()
• Removed the "Chosen" library.
• Improved and reduced the footprint on the Users admin screen, now allowing to filter by one or multiple groups.
• Added a welcome screen.
• Added the option to assign groups to new users directly when creating them from the Dashboard.
• Changed the language domain to string literal instead of constant.
• Improvements on internal coding standards (single/double quotes, EOF, formatting).