[ci] Setup CI build with sourcehut

Disable deprecated gtkmm-2.4 API, add CFLAGS required for gtkmm

Remove use of deprecated gtkmm-2.4 API, require gtkmm-2.4 ≥ 2.18

Remove redundant copy constructor

Upgrade CMake via brew in macOS Travis build.

Clearer naming for build system switching.

Require CMake >= 3.12, install cmake via brew in macOS Travis build.

Install librsvg before macOS build.

Rename RSVG variable to fix Travis CI build.

Install rsvg-convert tool in Travis build.

Explicitly specify destination for application binary.

CMake < 3.13 compat.

Use CMake in Travis build as well.

Install SCons on Travis-CI/Linux.

Update copyright.

Add files to support building with CMake.

sonar-scanner doesn't seem to be working with SCons.

Add sonar-project.properties for sonarcloud

Enable sonarcloud code scanning

Add image linking to current build status.