Add install rules and metadata for GTK/Linux

This allows to install Flips on Linux desktops, with all the modern
bells and whistles, like SVG icons, AppStream metadata, a flatpak
manifest, and the com.github.Alcaro.Flips reverse domain name app ID.

data/com.github.Alcaro.Flips.desktop

@@ -0,0 +1,15 @@
+[Desktop Entry]
+Name=Flips
+GenericName=Patcher
+Comment=A patcher for IPS and BPS files
+# Translators: Search terms to find this application. Do NOT translate or localize the semicolons! The list MUST also end with a semicolon!
+Keywords=ips;bps;patcher;
+Exec=flips %U
+# Translators: Do NOT translate or transliterate this text (this is an icon file name)!
+Icon=com.github.Alcaro.Flips
+Terminal=false
+X-GNOME-SingleWindow=true
+Type=Application
+StartupNotify=true
+Categories=GNOME;GTK;Utility;RevisionControl;
+MimeType=application/x-bps-patch;application/x-ips-patch;