Label now uses 'textContent' instead of 'innerHTML'

This change could break some uses of Label.

If you have special characters or HTML elements in your Label contents then they will no longer work (it will render them as plain text). This is to plug a security hole where by malicious code could be injected into a TAL label and executed.

Note: There is an alternate function on Label called 'unsafeSetHTMLText', this will apply the Label contents using 'innerHTML' (equivalent to Label.setText previously).