Skip null values on insert
Fix tests checking default values that don't exist
showInEditStrip -> showIn

Instead of boolean ‘showInEditStrip’, we are now using an array
‘showIn’ which uses the formBuilder::TYPE_* constants to determine if
something should be shown in that form. Default is all.

Example (only shows in update and edit forms):
$form->addField(array(
  ‘name’ => ‘foo’,
  ‘showIn’ => array(formBuilder::TYPE_UPDATE, formBuilder::TYPE_EDIT)
));
:racehorse: Reorder skips for performance