Re-create the zeal plugin

Hi,

I was looking at the Phabricator and I found an unfinished PR about the zeal plugin. I took my time to recreate the changes manually (I couldn't apply the diff file) and I created a PR here.

I didn't alter anything from the last diff*, although the indentation is messed up now. So, if you agree on this plugin, let me know what must be done for it to be accepted.

Coding plugins for KDevelop isn't my "forte" so I can't really understand or code further the plugin. But I can indent the code, or comment the parts I do understand etc.

So, I am going to need some help on this. Thank you very much in advance.

*EDIT: I forgot to mention that because of many compile errors, I did alter some of the code just not feature-wise.