ENH: Add specific HTTP errors for 403 and 404

Should be used instead of the corresponding Entity Errors that are
currently misused as connection errors.

src/caosdb/exceptions.py

@@ -59,6 +59,9 @@ class ConfigurationException(CaosDBException):
     _INFO = ("\n\nPlease check your ~/.pycaosdb.ini and your $PWD/"
              ".pycaosdb.ini. Do at least one of them exist and are they correct?")
 
+# TODO: Group the following errors (until TransactionError) according
+# to their HTTP codes as children of client/server exception.
+
 
 class ClientErrorException(CaosDBException):
     def __init__(self, msg, status, body):
@@ -110,6 +113,26 @@ class LoginFailedException(CaosDBException):
         CaosDBException.__init__(self, msg=msg)
 
 
+class UnauthorizedException(CaosDBException):
+    """You're lacking the required permissions. Corresponds to HTTP status
+    403.
+
+    """
+
+    def __init__(self, msg=None):
+        CaosDBException.__init__(self, msg=msg)
+
+
+class ResourceNotFoundException(CaosDBException):
+    """The requested resource doesn't exist; corresponds to HTTP status
+    404.
+
+    """
+
+    def __init__(self, msg=None):
+        CaosDBException.__init__(self, msg=msg)
+
+
 class TransactionError(CaosDBException):
 
     def _calc_bases(self):