[FEATURE] Export Area as under "Subject areas" tab and in "Presentation Mode"

[BaccanoMob]

"Export as" is a really good feature under File menu but it only exports the viewable part of the drawing. Larger (or spaced out) diagrams may take multiple takes trying to resize and squeeze into the screen.

I rather put a (temporary) area covering everything and then choose that area to export. It minimizes the time I try to fit everything into screen since I just have to drag the corners to mark the boundaries. Note that the area fill should become transparent for the export.

This also acts a bonus if someone wants to export a particular area alone. That is, you will not need to crop the extra bits (aka outside of area) when exporting.

Currently in presentation mode below icons are visible,

It would be great if there was an export as icon as well. Since this mode maximizes the visually area and better idea how the export will actually look like, otherwise I need to have the menu bar open which takes some space on top.