month-cell: Rounded displayed weather forecast temperatures (in month / week view cells) to integers precision

In this commit, I have made several updates to improve the functionality of temperature values in GWeatherInfo, Weather-Service, and Month-Cell.

1. Updated GWeatherInfo to save temperature as a gdouble data type instead of a string. This change will improve the precision of temperature values and make it easier to perform logical operations and comparisons on temperature values. I have also updated the relevant functions and methods to accommodate this change in data type.

2. Updating Weather-Service to use gdouble data type for temperature, to ensure consistency and compatibility with the updated GWeatherInfo. I have converted the data type of temperature from gchar* to gdouble, and updated the relevant functions and methods to reflect this change.

3. Updating Month-Cell to round off temperature values to integer precision, as required by issue #982. With the updated GWeatherInfo and Weather-Service, we can now easily implement this functionality in Month-Cell by rounding off temperature values to the nearest integer using the appropriate rounding function.

Screenshot