add option to disable GZ compression for HDD caching

Related to request from WP support forums: https://wordpress.org/support/topic/disable-gz/

The HDD caching module always generates a static HTML file along with a gzipped version:

cachify/inc/cachify_hdd.class.php

Lines 165 to 166 in dcac6b7

    
           self::_create_file( self::_file_html( $file_path ), $data ); 
        
           self::_create_file( self::_file_gzip( $file_path ), gzencode( $data, 9 ) );

We have a corresponding block in the Apache HTTP server example using mod_mime to server the pre-compressed content.

With most webservers supporting compression natively which can be superior to compression by PHP and more important is not handled during initial site visit, many sites don't need the explicit *.gz files.

We should at least introduce an option to disable generation of pre-compressed files to reduce the overhead here.

What about trying to detect if gzip is enabled, to automatically deactivate the encoding?

#262 This PR addresses this issue.

	self::_create_file( self::_file_html( $file_path ), $data );
	self::_create_file( self::_file_gzip( $file_path ), gzencode( $data, 9 ) );