Refactor helpers to return unicode strings
Make sure that CLI always deals with unicode.

To make it simpler and safer to use strings via CLI, all data that gets
passed to Paramiko gets encoded to UTF-8 and all data returned from
Paramiko gets decoded to unicode.
Removed print statements.
Fix StringField to aways return unicode strings
Merge pull request #536 from elyezer/unicode-refactor

Fix StringField to aways return unicode strings
Remove unnecessary if statement
Merge pull request #541 from elyezer/unicode-refactor

Remove unnecessary if statement
Merge pull request #540 from omaciel/unicode-refactor

Unicode refactor