Goals: Remainder option (#1101)

Added the option to add a remainder goal template. This will use the
remaining available funds and dump them into the respective category.
There is optional weighting. The remainder templates will be forced to
the lowest priority as to run after all other templates.

Usage: `#template remainder <weight>` Add the template line to any
categories you want to catch any remaining funds such as savings. The
amount added to the category will equal
`remaining_budget/total_of_weights*weight`. The default weight is 1.