applets/weather: Show forecast in two rows for envcan provider

The envcan provider (Environment Canada Service) produces a
forecast model with 13 items (7-day forecast and 6 nights).

Show them on a two row layout, so its easier to visually parse
and helps avoiding visual bugs on constrained spaces (system
tray popup) due to a really long width.

Ideally, this would be better set-up by the dataengine but,
since they will be deprecated soon and there are alreay too many
indirection layers we can do an educated guess here.

BUG: 452792
BUG: 394809
FIXED-IN: 5.27