Fixed Crypto errors and uncaught exceptions

The crypto salt file is no longer a thing. Now the salt is merely
appended to the `crypt_file` as the last sixteen bytes. The salt
is read from the end of the `crypt_file` on subsequent decryptions.

Added a setting for enabling 'debug' mode, using `pdb` for dynamic
debugging in pappy sessions. When needing to debug a function, or
set of functionality add the conditional `if config.debug`, then
set an entry point for `pdb` using `import pdb; pdb.set_trace()`
May remove this functionality if not desired in the main project.

pappyproxy/config.py

@@ -164,6 +164,7 @@ class PappyConfig(object):
         self.global_config_dict = {}
 
         self.archive = 'project.archive' 
+        self.debug = False
         self.crypt_dir = 'crypt'
         self.crypt_file = 'project.crypt'
         self.crypt_session = False