Add a test method to download client and libraries.

Add a simple File object to simplify certain file operations.

INFO: Libraries are unfiltered. Some of the library that for other platform will be downloaded too.

core_lib/common/exception.py

@@ -0,0 +1,15 @@
+from pathlib import Path
+
+
+class LauncherException(Exception):
+    def __init__(self, message):
+        self.message = message
+
+    def __str__(self):
+        return self.message
+
+class HashMismatchException(Exception):
+    def __init__(self, hash_name, got_hash, expected_hash, filepath: str | Path):
+        if type(filepath) == Path: filepath = Path(filepath).absolute().as_posix()
+        self.message = "File {} hash mismatch. Expected hash {}. Got hash {} ({})".format(filepath, got_hash,
+                                                                                          expected_hash, hash_name)