Automatically drop .gla extension in glm header

Users are now free to include .gla in the gla reference export setting,
it will be dropped automatically to ensure the game can load the file.

Fixes #51.

JAG2GLM.py

@@ -989,7 +989,8 @@ def loadFromFile(self, filepath_abs: str) -> Tuple[bool, ErrorMessage]:
 
     def loadFromBlender(self, glm_filepath_rel: str, gla_filepath_rel: str, basepath: str) -> Tuple[bool, ErrorMessage]:
         self.header.name = glm_filepath_rel.replace("\\", "/").encode()
-        self.header.animName = gla_filepath_rel.encode()
+        # the .gla extension must be omitted
+        self.header.animName = gla_filepath_rel.removesuffix(".gla").encode()
         # create BoneName->BoneIndex lookup table based on GLA file (keeping in mind it might be "*default"/"")
         defaultSkeleton: bool = (gla_filepath_rel ==
                                  "" or gla_filepath_rel == "*default")