move StructParam to frappy/extparams.py

+ typos and fixes in doc strings

Change-Id: Ib3e9add84ce2a6fb5c33770cae7f2da3f5655506
Reviewed-on: https://forge.frm2.tum.de/review/c/secop/frappy/+/33033
Tested-by: Jenkins Automated Tests <pedersen+jenkins@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

test/test_extparams.py

@@ -24,8 +24,7 @@
 from test.test_modules import LoggerStub, ServerStub
 import pytest
 from frappy.core import FloatRange, Module, Parameter
-from frappy.structparam import StructParam
-from frappy.extparams import FloatEnumParam
+from frappy.extparams import StructParam, FloatEnumParam
 from frappy.errors import ProgrammingError