Bentso

* Added trade to non-ENTSO countries and missing internal trade links
* Added missing countries
* Fixed rescaling of `Other` to be time-interval specific instead of yearly average
* Added more generation dataframe cleaning functions
* Added option patch to Latvia to rename `Other` to `Fossil oil`
* Raise `ValueError` if ENTSO API call fails

* Added functionality to downscale data to hourly resolution
* Added functionality to fill out complete years using average data in place of missing values

Add some constants for countries and trade

Delete debugging statement

Added ability to clean dataframes

Fix missing package metadata files