Bug 1019595 - Use light cancel edit button with dark lightweight themes. r=bnicholson

--HG--
rename : mobile/android/base/resources/drawable-hdpi/close_edit_mode.png => mobile/android/base/resources/drawable-hdpi/close_edit_mode_light.png
rename : mobile/android/base/resources/drawable-mdpi/close_edit_mode.png => mobile/android/base/resources/drawable-mdpi/close_edit_mode_light.png
rename : mobile/android/base/resources/drawable-xhdpi/close_edit_mode.png => mobile/android/base/resources/drawable-xhdpi/close_edit_mode_light.png