Add icons representing types

[kazagistar]

Consider adding icons to represent type more semantically? This will solve confusion about which type something is, without causing too much confusion for users.

Here are some ideas from the Bootstrap Glyphicons (which was on hand as some examples):

• string: icon-comment
• number: icon-calculator
• object: icon-folder-open
• array: icon-list
• true/false: icon-check
• null: icon-asterisk