build: Added AppImage builder (#355)

* Docker files to create an AppImage

* Using ENTRYPOINT is a bit nicer here

* typo

* put with other dist files

dist/AppImage/extract.sh

@@ -0,0 +1,26 @@
+#!/bin/bash
+
+# Set the TAG environment variable to move to a versioned name while extracting
+
+# Make sure we're in the same direcotry as this script
+pushd $(dirname "$(realpath "$0")")
+
+# Remove old containers
+docker rm imhex 2>&1 > /dev/null
+
+# AppImage uses FUSE, which makes --device /dev/fuse --cap-add SYS_ADMIN necessary here
+# on Debian --security-opt apparmor:unconfined is also needed
+if [ -z "$TAG" ]; then
+    docker run -d --device /dev/fuse --cap-add SYS_ADMIN --security-opt apparmor:unconfined --name imhex imhex-appimage-build
+else
+    docker run -d --device /dev/fuse --cap-add SYS_ADMIN --security-opt apparmor:unconfined --name imhex imhex-appimage-build-$TAG
+fi
+sleep 10
+docker cp imhex:/ImHex-x86_64.AppImage .
+
+# Move to tagged name if $TAG set
+if [ -n "$TAG" ]; then
+    mv ImHex-x86_64.AppImage ImHex-${TAG}-x86_64.AppImage
+fi
+
+popd