[FE] [FEATURE] - Add loader during HTTP calls

[Roberto286]

We need to implement a loader/spinner during http calls. The basics prerequisites are:

• Since we are not using a components library we could make our custom spinner using only HTML and CSS. Examples here: https://loading.io/css/
• The loader should be visible from the moment that the HTTP starts to when the HTTP response + the subsequent logic are done
• The UI should be blocked when the spinner is shown, so the window should not be able to listen for click events