Add gpx type, fix file replacement

CHDataManagement/Model/FileResource.swift

@@ -108,7 +108,11 @@ final class FileResource: Item, LocalizedItem {
     }
 
     func save(textContent: String) -> Bool {
-        content.storage.save(fileContent: textContent, for: id)
+        guard content.storage.save(fileContent: textContent, for: id) else {
+            return false
+        }
+        modifiedDate = .now
+        return true
     }
 
     func dataContent() -> Foundation.Data? {