Refactor CMakeFiles

Summary:

• Use ECM for adding tests
• Use consistent naming for CMake functions
• Only add tests when adding -DBUILD_TESTING
• Code formatting
• Use option for options
• Use ECM for version number and change version number from 2.49.beta to 2.49.90

Test Plan: make -j8 install works and make test too

Reviewers: niccolove, iasensio, alex

Reviewed By: niccolove

Differential Revision: https://phabricator.kde.org/D29718