Multi Prefix 2.16.3

Update installer to better handle very large number of threads upgrading

Remove leftover select2 css

• Improve "article forum" compatibility and multiple filters being clickable filters
• Fix clickable filtering prefixes where added to the watched thread list when watched threads filtering add-on is not enabled/installed

• Fix API support for @XenConcept's Project Manager not working as expected
• Support displaying multiple prefix descriptions in a thread

• Fix support for XF2.2+ suggestion forums implemented/closed prefixs selection working with threads with multiple prefixes

• Work-around php8 compatibility bug in prefix rendering

Update minimum supported versions for;

• DbTech Shop v6.4.3+
• DbTech eCommerce v2.2.3+