Modify HTTP logs in clients for safety and clarity

Refs grnet/kamaki#32

Implement method escape_ctrl_chars
Escape control characters in HTTP data logs
Remove misleading separators from HTTP logs
Remove dysfunctional decoding (kamaki.cli.cmds)

Refs grnet/kamaki#32

String decoding was used to deal with unicode strings, which were
encoded as "unicode_escape" in earlier steps. The later was wrong and
it was fixed with 18d5b0539dcf146d3b9b23fe8e4f4ade6d6dc867
The present commit completes the fix by undoing the decoding.
Escape characters in CLI output methods

Closes grnet/kamaki#32

Kamaki CLI commands use some generic output methods to handle outputs.

Generic output methods that escape control characters:
- in kamaki.cli.utils: print_items, print_dict, print_list
- in kamaki.cli.cmds: error

Generic output methods that don't escape control characters:
- in kamaki.cli.cmds: writeln, write

The methods that don't escape control characters are used when the
standard methods are not sufficient. For example, in "kamaki.cli.pithos"
the "PithosAccount.print_objects" method adds decorative escape characters
(i.e., bold, alignment), but has to escape the parts object and container
names. To achieve this, escaping is handled in the method, and the output
is printed with the "write" and "writeln" methods mentioned earlier.

An encoding issue with kamaki.cli.errors.CLIError and the Exceptions extending it,
is fixed. It is now ensured that the error message will always me in unicode.

Also, fix flake8 errors on files affected by the above changes