NEW: Support for multiline mode in CPTextField

This patch adds support for CPTextField with multiline content. It uses
a DOM textarea when needed, instead of DOM input.

It also disable the spellchecking, fixes a bug where the input element was not
correctly resized when the frame changed, and refactor some code
Add support for usesMultilineMode and fix wraps and scrolls in nib2cib
Add manual test
Add CPAltEnterTextAreaFeature checking. FF doesn't add a cariage return on textarea when doing alt+enter
Merge pull request #2257 from primalmotion/textfield-multiline-support

NEW: Support for multiline mode in CPTextField