[member function] Changed get_nodeattr_types by moving "backend" attribute to __init__ instead of in each fpgadataflow custom op class

[Verify CustomOp Construct] Deleted obsolete file, because functionality is now moved to CustomOp class

[StreamingFCLayer_Batch] filled verify function and extended get_nodeattr_types with backend, code_gen_dir and executable_path

[StreamingMaxPool_Batch] filled verify function and extended get_nodeattr_types with backend, code_gen_dir and executable_path

[Pre-commit] formatted files and changed the exception errors in verification to more detailed descriptions of the error