Refactor for better modularity (share more code among edit functions, rename "offline" package to "backend"

src/backend/targetLocationFormatUNIX.go

@@ -0,0 +1,8 @@
+//go:build !windows
+
+package backend
+
+// TargetLocationFormat returns the target location of an entry formatted for the current platform
+func TargetLocationFormat(entryName string) string {
+	return EntryRoot + PathSeparator + entryName
+}