Cleanup unused includes

So, I was bored, and went on to get rid of unused includes in Konsole.

I've used include-what-you-use tool with clang. Unfortunately there's a lot more left because there're false positives, besides suggestions by the tool are quirky (it often suggests to add the same include as it suggested to remove, but lower-cases the name), so using this tool is pretty tedious.

I mostly broke down changes in different files to distinct commits, just in case some change refuses to get built on some platform, then it would be easier to find the relevant change.