Added "Apply to text widgets"

Added option called filter_text_widgets
Update admin.php
Added lazy loading in text widgets

Added the option filter_widget_text
This option will enable users to lazy load stuff in the text widgets.

(You know .. those pesky little widgets that has 99% of the images and iframes ..)
Merge pull request #4 from sigginet/master

Added the option to lazy load in text widgets. Thanks Sigurður Guðbrandsson