Refactor logic for importing scapy related functions

* Make scapy related requirements less strict
* Always print out a useful error message when something goes wrong
(cherry picked from commit 77b2f6e7206f5a1bb1531fb2416eaf36675b098b)
Update before_i_commit script to make it work
(cherry picked from commit 9cdf5596c8f16cac819afdaf1b9b537b36f796a6)
Return something in txscapy
Merge pull request #57 from hellais/bugfix/imports_and_before_i_commit

Bugfix/imports and before i commit