Future patches

[mightyaleksey]

• [ ] Replace Tumbler's box-shadow's with borders: http://sullenor.github.io/teatime-components/#Tumbler. Another issue with zooming.
• [x] Wrap spin to avoid transform issues.
• [x] Check the possible restriction for the string only for the children props on components. Should be PropTypes.node.
• [x] Add the jsfiddle example.
• [x] Update props types.
• [x] Issue with blur and focus events for input.
• [x] Consider adding support of the nullable values (presumably, convert it to the empty string).