Replace receiving countries' information with open API

[Pareder]

For "Details mode" the hardcoded countries' information (capital, language, population, etc.) is used that is stored in public/json/custom.json file and needs to be updated periodically. Not to depend on self-hosted file there is a need to find an open API which will return up-to-date information about countries. When finding this API add functionality to fetch it when clicking on certain country in "Details mode" instead of showing hardcoded properties.

Pay attention to filters section at the top of the "Details mode" page.