what kind of language you are using?
only javascript (browser based)? or PHP/asp (server based)?
if only JS: http://stackoverflow.com/questions/15005500/loading-cross-domain-html-page-with-jquery-ajax
if PHP, use "file_get_contents" and http://php.net/manual/en/class.domdocument.php
What about server side includes? Is your site running apache? Barring this and JS hackery, you would need to dig deeper into the rabbit hole and learn a server side programming language.
There are several *AMP type packages that can get you up and running with a quick install.
XAMPP has been the popular choice for a while but the newwer updates have been buggy for me. I recently migrated my local dev to EasyPHP and have been happy so far.
Hey; I think what you're do may not be a good idea so to speak. Generally publishing your api key is a bad idea. Consider that an api key allows you to do anything you can (within the scope of your permissions). There are exceptions though. It depends what it lets you do and how much someone else could abuse it. There was a great discussion about this on hackernews. https://news.ycombinator.com/item?id=9557298
The curly brackets and everything between represent a serialized and URL escaped JSON object.
>decodeURIComponent( location.href ) -> > "https://www.gumtree.com/search?q=tables&tq={"i":"tables","s":"tables","p":0,"t":15}&search_category=home-garden&search_location=&distance=0.0001"
This isn't exactly a very easy thing to do. There are tools out there than can provide similiar to what you are looking for (http://www.dnsmadeeasy.com/), however i have never used them to know for sure if they will solve your problem.
I know cloud hosting services such as Heroku do this, however i do not know how they have their systems configured to handle it. You may be able to research about how Heroku is setup if you really wanted to try and configure this yourself. I would assume that if you do not have full root access to your servers / dns server, it would be very difficult to do.
The MEAN stack is a good idea, but if you don't want to learn all those things at once, you can leave out Angular for now. Here is an idea of how you can set it up:
Set up a Nodejs server with Express on it. Look up some tutorials online, its very simple and there is even a generator utility for it that generates an express project for you. Set up some routes for your api that you can make requests to in the routes file. Set up your db of choice up and look up how to access it from Node. Make your database functions (i.e add content, remove, update, etc). Call those functions from the routes that you have set up, so that when the server gets a request on a route it makes the appropriate call to function. Finally, make your api calls to the servers (to the routes you set up) from your front end and profit!
I have explained it very simply to just give you an idea of how things will be. You will obviously need to learn these things to get a better understanding. The Express docs are very nicely organized so just refer to those if you need help and don't be afraid to google!