Add the option to display whole values instead of showing unnecessary fractions in decimals

[chrisK00]

Background

This is how decimal values are presented in subtrack right now:
$ 10.50
$ 10.00
$ 2.00

Most of the time we are interested in only the whole number and in some countries such as Sweden prices are commonly only in whole numbers. We should make it optional wether the fractional part in the decimal should be displayed.

If the option is on the above costs would be displayed as
$ 10
$ 10
$ 2

Tips

• The feature Import and Export Subscriptions #137 has issues regarding creating the settings page and adding options. Use as reference
• When fractions are displayed it would be nice if the fractional part (including the dot ".") would have a smaller font size so that it is less noticeable, same as how amazon does it.
  

Acceptance Criteria

• The option is added to the settings page as a toggle named "Hide Fractions". Default value is off so that fractions are displayed by default
• Index, Monthly, Details, and Upsert page are updated according to wether the setting is on