Don't put method definitions in the header file of XdgShellClient class
as it makes the code visually inconsistent. InternalClient is a good
example of how the header file of a subclass of AbstractClient class
should look like.
This change also cleans up the order of things in the header file, thus
making it a bit more obvious where new things should go.
Summary:
Rename ShellClient to XdgShellClient in order to reflect that it
represents only xdg-shell clients.
Test Plan: Compiles, tests still pass.
Reviewers: #kwin
Subscribers: kwin
Tags: #kwin
Differential Revision: https://phabricator.kde.org/D23589
Vlad Zahorodnii