SemaSCDG.py crashes when enabling plugin_hook

[Thib-fkr]

(this fix includes part of the Pull request#42 for being able to enable the plugin-hook)

When enabling plugin_hooks, the parameter self.content passed to PluginHook.py is of type str, where it is expected to be bytes.

  File ".../sema_scdg/application/SemaSCDG.py", line 475, in setup_hooks
    self.plugins.enable_plugin_hooks(self.content, state, proj, self.call_sim)
  File ".../sema_scdg/application/plugin/PluginManager.py", line 53, in enable_plugin_hooks
    self.hooks.initialization(content, is_64bits=proj.arch.name == "AMD64")
  File ".../sema_scdg/application/plugin/PluginHooks.py", line 59, in initialization
    pe_header = int.from_bytes(cont[0x3c:0x40],"little")
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
TypeError: cannot convert 'str' object to bytes

The proposed fix initializes SemaSCDG's self.content property as a byte string.