Feature: Include page border when exporting

[Thangalin]

In the Export Bitmap dialog, it would be nice if there was one more checkbox:

- Include Page Border

When checked, clicking "Export" would include the page border in the output. This is useful when presenting a full page, including the border, that has annotations around it. Currently when exporting the "Selection" (i.e., everything inside the page border and everything outside -- such as the annotations), the page border disappears.

The effect is that it is difficult to visualize how the content fits on the page with respect to the page border.

Two work arounds include: (1) take a screen shot of Inkscape, which will include the page border; and (2) add a fake page border object.