Clean up Kate addons CMake scripts.

Summary:
This is the first in a series of revisions modernizing the Kate CMake scripts.
I'm submitting the changes to the addons directory first as they form a
nicely separated list of changes.

Note that if https://phabricator.kde.org/D22698 and
https://phabricator.kde.org/D22699 are merged, most if not all of the
remaining source lists in the addons directory can be removed in favor of
working with targets.

List of changes made:

• Standardize style on two spaces and no whitespace between commands and arguments.
• Remove directory commands in favor of target-based commands as recommended by modern CMake.
• Remove usage of qt5_add_resources in favor of CMAKE_AUTORCC and adding .qrc files directly to a target's sources.
• Remove usage of source lists (where possible) in favor of CMake 3.1's target_sources command.
• Remove the CMake binary directory as an include directory from most addons.
• Remove unnecessary comments, CMake project calls, config files, etc from addon CMake scripts.
• Remove HAVE_CTERMID from config.h and move the check and addition to compile definitions to the project addon CMake script as its only used in the project plugin sources.

Test Plan: Apply changes and verify Kate still builds and works exactly as before.

Reviewers: Kate, cullmann

Reviewed By: Kate, cullmann

Subscribers: cullmann, kossebau, turbov, asturmlechner, kwrite-devel

Tags: Kate

Differential Revision: https://phabricator.kde.org/D22721