Add support for units for the numeric properties

[vaspa]

It is hard to align some numeric values and their units on the screen. Even impossible if "left" or "center" number alignment is used. You may also want to have the same font style and avoid creating special images.

Use case examples:

• battery level + "%"
• humidity + "%"
• heart rate + "bpm"
• temperature + "°C"
• etc.