Templatization of forum stats page

[rica-carv]

Motivation and Context

Enable templatization of the forum stats page. It's hard to customize hardcoded HTML inside PHP files...

Description

Changed forum_stats file to enable use ot template files and shortcode file.
NOTE: Files still need cleanup, to do after more tests from another users

How Has This Been Tested?

Tested with e107 v2.3.3

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation (a change to man pages or other documentation)

Checklist

• My code adheres to the e107 code style standard.
• I have read the contributing document.
• I have added tests to cover my changes.
• All new and existing tests pass.