Enhance compatibility

Adding the path to '.settings.pkl' file, this is especailly useful for MacOS. Then we can put '.settings.pkl' into 'MacOS' folder within 'labelImg.app'. The App will crash without path setting, as soon as we close the App in MacOS.

libs/settings.py

@@ -1,10 +1,11 @@
 import pickle
 import os
+import sys
 
 class Settings(object):
     def __init__(self):
         self.data = {}
-        self.path = '.settings.pkl'
+        self.path = os.path.join(os.path.dirname(sys.argv[0]), '.settings.pkl')
 
     def __setitem__(self, key, value):
         self.data[key] = value