precipitation display changes; forecast style3

[shuu01]

Features:

• option to show or hide rainfall value on the precipitation label #178
• option to show or hide precipitation probability value on the precipitation label #178
• don't show precipitation label if both options from above are off #178
• precipitation type now only affects precipitation bar #178
• precipitation tooltips now always show both rainfall and probability
• option to change precipitation label font size
• option to completely disable graph tooltips
• add style3 forecast chart style, with rounded temperature and precipitation label borders