Supports loading config flags from file, other suggested fixes.

- supports --config-file <file> option.
- cyrpto_util has no os specific code. Mac's DYLD_LIBRARY_PATH check moved to openbazaar_daemon.py
- suggested fixes on comments.
- fixes import issue on test_transport.py

Still to do:
 `$ openbazaar stop`
 `$ openbazaar status`