Remove double underscore (__) from header include guards
Summary:
Names containing a double underscore (__) are reserved to the
C++ implementation, so better just avoid it, even with KATE namespace.
Needs rename of global config include guards to avoid guard name clash.
Test Plan: Still builds
Reviewers: Kate, cullmann
Reviewed By: Kate, cullmann
Subscribers: cullmann, kwrite-devel, kde-frameworks-devel
Tags: Kate, Frameworks
Differential Revision: https://phabricator.kde.org/D16300