Missing dependencies error message

[parsa]

Problem

User has to read the traceback to figure what's missing

$ ./scimitar.py
Traceback (most recent call last):
  File "./scimitar.py", line 21, in <module>
    from sessions import modes, offline_session, debug_session
  File "C:\Users\Parsa\Documents\scimitar\scimitar\sessions\__init__.py", line 12, in <module>
    import modes, offline_session, debug_session
  File "C:\Users\Parsa\Documents\scimitar\scimitar\sessions\offline_session.py", line 14, in <module>
    import pexpect
ImportError: No module named pexpect

Proposed Solution

1. Warn the user if dependencies (pexpect, prompt_toolkit, etc) are not installed.
2. Create wheel/egg