Flatpak build support (#112)

* Use XDG_CONFIG_HOME

* Migrate from config v0 to v1

* Start work on Flatpak packaging

* add Keywords, StartupNotify and improve the Comment

* Sync w/ upstream flatpak branch

* Fixes for egui transition

* More flatpak fixes

* Fix icon error

* add itch folder to permissions

* Fix main after rebase

Co-authored-by: casept <davids.paskevics@gmail.com>
Co-authored-by: jrt <git@jrtberlin.de>

flatpak/dk.philipk.BoilR.desktop

@@ -0,0 +1,13 @@
+[Desktop Entry]
+Version=1.0
+Type=Application
+
+Name=BoilR
+Comment=Add non-steam games to your steam library
+Categories=Utility;Amusement;
+Keywords=Steam;Heroic;Lutris;Itch;Origin;GOG;UPlay;Icons;Images;Non-Steam;Games;
+
+Icon=dk.philipk.BoilR
+Exec=boilr
+Terminal=false
+StartupNotify=true