Reject raw files without padding if discard partial is not set (#374)

We have no code in aare to deal with RawFiles that have missing packets
if they are not padded to full size or frames with packet loss dropped.

Added: 
- check that we don't try to read files that are not supported
- python bindings for frame discard policy

at least we get the check in: 
closes #171

---------

Co-authored-by: AliceMazzoleni99 <alice.mazzoleni@psi.ch>

src/RawMasterFile.cpp

@@ -546,9 +546,8 @@ void RawMasterFile::parse_raw(std::istream &is) {
                 m_image_size_in_bytes = std::stoi(value);
             } else if (key == "Frame Padding") {
                 m_frame_padding = std::stoi(value);
-                // } else if (key == "Frame Discard Policy"){
-                //     m_frame_discard_policy =
-                //     StringTo<FrameDiscardPolicy>(value);
+            } else if (key == "Frame Discard Policy") {
+                m_frame_discard_policy = string_to<FrameDiscardPolicy>(value);
                 // } else if (key == "Number of rows"){
                 //     m_number_of_rows = std::stoi(value);
             } else if (key == "Analog Flag") {