createCheckable should always return a string.
Add tests to avoid bad implicite to string Checkable conversion.
Fix bind for checkables.
Merge pull request #399 from menthol/fix-bind-for-checkable

Fix bind for checkables.
Merge pull request #395 from menthol/develop-element-render

createCheckable should always return a string.
Fix #396, Allow manualy created checkables.