Adding backgrounds using page events

Examples written in answer to questions such as:

• Click How to change the color of pages?

• How to draw a border for PDF pages?

pagebackgrounds

##GITHUB:https://github.com/itext/i7js-examples/blob/develop/src/main/java/com/itextpdf/samples/sandbox/events/PageBackgrounds.java##

##GITHUB:https://github.com/itext/i7ns-samples/blob/develop/itext/itext.samples/itext/samples/sandbox/events/PageBackgrounds.cs##

pageborder

##GITHUB:https://github.com/itext/i7js-examples/blob/develop/src/main/java/com/itextpdf/samples/sandbox/events/PageBorder.java##

##GITHUB:https://github.com/itext/i7ns-samples/blob/develop/itext/itext.samples/itext/samples/sandbox/events/PageBorder.cs##