* A *lot* of import fixes for flatpak
Aside, thank you @hadess for the majority of these fixes. You are the
base point for a lot of issues fixed during the creation of this
flatpak.
* Use slic3r::load_string_file
Boost 1.84 removed `boost::fs::load_string_file` so use the func located
in Utils.hpp
Add the option to use non-relative extrusion in printer config screen. Some extruders do not play well with relative extrusion...
Remove reference to multi-extruder
Remove reference to multi-extruder
change g-code comment for M83 relative extrusion
changed comment for M83
Remove commented line of code
In this specific case, we delete the old line of code because it refers to a variable that was deleted from the rest of the code (RELATIVE_E_AXIS)
