Clean version management with generated version.js

- Replace package.json modification with generated src/version.js
- App imports VERSION from ./version instead of package.json
- version.js is auto-generated during prebuild and git-ignored
- Provides VERSION, IS_RELEASE, and BUILD_TIME constants
- No more dirty git status from version changes

Development builds show 1.0.4-dev, tagged releases show 1.0.4

.gitignore

@@ -22,6 +22,9 @@ npm-debug.log*
 yarn-debug.log*
 yarn-error.log*
 
+# Auto-generated version file
+/src/version.js
+
 # IDE
 .vscode/
 .idea/