Allow shell quoting on CLI

Break up command-line args using shlex rather than string.split

This enables multiple-word tags using quotes:

mailpile> tag/add "three word tag"
mailpile> tag +"three word tag" 20
Merge branch 'tags' of github.com:danohuiginn/Mailpile into pull-zone

Conflicts:
	mailpile/commands.py
	mailpile/plugins/tags.py
Fix mistakes made merging the shlex stuff
Make shlex the default argument splitter
Merge branch 'pull-zone' - shlex ftw!
Adding pyside experiment to scripts/
PEP8 and return message cleanup (issue #383)