Add a new method to Figure to shift the plot

[leouieda]

Description of the desired feature

Unlike tools like matplotlib, GMT plots things to a canvas/page using physical coordinates. You can control where the plot is placed on this canvas with the X and Y arguments. Traditionally, if you want to shift the origin to another location, you'd call gmt plot -T X=... Y=.... The -T served tell plot to not actually plot anything. This is a bit unnatural and we should probably not allow the -T option. Instead, we should have a method like Figure.shift_origin that does this by calling plot. See #253

Are you willing to help implement and maintain this feature? Yes

[leouieda]

This is not a priority right now and will probably only be used for more advanced plots.