Refactor codebase with new method for determining hostname

[raamdev]

@jaswsinc writes...

There are actually a few places where we use $_SERVER['HTTP_HOST']. As of now, that needs to change I think, overall.
https://github.com/websharks/zencache-pro/search?utf8=%E2%9C%93&q=%24_SERVER%5B%27HTTP_HOST%27%5D

It would be nice to have a new method that deals with working out what domain should be used.

I see us needing a new file in this folder called HostUtils.php
https://github.com/websharks/zencache-pro/tree/6e6d2f7d8a4c992dd61a4ed59d3dc326cc829692/src/includes/closures/Shared

Inside HostUtils.php, we could create a new method that might be named something like:

$self->httpHost = function($consider_domain_mapping = true) use ($self) {
    // That code snippet could go here, and we might need some additional logic and perhaps a function parameter or two. e.g., $consider_domain_mapping
};

With that in place, we can start updating the rest of the codebase, replacing references to $_SERVER['HTTP_HOST'] with calls to this method.

Forked from #339 (comment)

[jaswrks]

@raamdev Are you still planning to work on this or do you want me to take it?

[raamdev]

@jaswsinc You can take it if you'd like. Thanks!

[jaswrks]

Referencing: #339 (comment)

[raamdev]

Closed by PR wpsharks/comet-cache-pro#125. See related changelog entry: #339 (comment)