Add a frontend for compiler-explorer

This change introduces a new plugin: Compiler Explorer. The main purpose of this plugin is to allow you to view the generated code of any file in your project easily. You can do that in Compiler-Explorer but it takes a lot more effort and you have to copy over flags etc.

To use this you obviously need some Compiler-Explorer instance for e.g., the godbolt.org website or a local instance of your own which is pretty easy to set up.

Right now there isn't any obvious "context-menu" action to view the asm mainly because I am not really sure where to put it yet and also because I need to test this a little more. So, to use this, one can open it via "Alt + Ctrl + i" and then type "Compiler" and it will give you the action which will launch CE for whatever your last KTE::View was. You can then press "Compile" and it will compile the code.

Besides the plugin itself, there is a major change packed in i.e., the ability to allow any QWidget in Kate's tabs. One big reason for developing this plugin (besides the obvious use case) was to explore the ability to host arbitrary widgets in Kate's tabs. This can give us a lot of super powers very quickly i.e., a proper large diff view, big terminal, web browser (kidding ;p).