add an installation script

[taj-ny]

This should make installation more user-friendly, also it allows me to remove submodules from this repo.

Usage: ./install.sh [options]

Options:
  --ctl                         Build the control tool
  --ctl-branch <branch>         Build a custom Git branch of the control tool (checks out the specified branch)
  --kwin                        Build the KWin implementation (mutually exclusive with --standalone)
  --kwin-branch <branch>        Build a custom Git branch of the KWin implementation (checks out the specified branch)
  --standalone                  Build the standalone implementation (mutually exclusive with --kwin)
  --standalone-branch <branch>  Build a custom Git branch of the standalone implementation (checks out the specified branch)
  --standalone-no-systemd       Disable systemd support

  --latest                      Build the latest Git commits of all projects (checks out the main branch)
  --latest-stable               Build the latest stable releases of all projects (checks out the latest tag or the main branch if there are none)

  -d,--debug                    Build the debug configuration
  -p,--package <generator>      Generate packages using the specified CPack generator instead of installing

  -h,--help                    Show this message and exit