GII - short echo syntax

As commented in https://github.com/yiisoft/yii2/issues/35#issuecomment-26755788

This is just in CRUD generator so you can review and make some comments if it's needed.
I tried to be consistent with the style, making some changes.
Everyithing echoed to the templates use double quotes, so it supports withespaces formatting, and kept the single spaces between these quotes.
For example:

```php
<?php foreach ($safeAttributes as $attribute) {
	echo "\t\t<?= " . $generator->generateActiveField($attribute) . " ?>\n\n";
} ?>
...
...
<?= "<?php " ?>ActiveForm::end(); ?>
```

Please review and point out the changes you consider so I can rework it.