#136: Move from qmake to CMake

[aaronhktan]

Description

This commit switches the project's build system from qmake to CMake.

Using CMake has several advantages:

• Looking forward, Qt 6 uses CMake by default. It will be easier to migrate to Qt 6 with CMake as the default build system.
• CMake is essentially an industry standard for C++ projects. This is a good learning opportunity, and because there are many people using CMake, it is easy to find resources for most edge-cases.
• Automatic discovery of tests whose build system is CMake-by-default.

Part of a series of commits for #136.

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Tested by building debug builds on macOS, Windows, and Linux. Packaging for release has not yet been tested, and will be tested once a release is closer.

Checklist:

• My code follows the style guidelines of this project (black for Python
  code, .clang-format in the src/jyut-dict directory for C++)
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have translated my user-facing strings to all currently-supported languages
• I have made corresponding changes to the documentation