Add an artificial delay to FiatCurrencySettings page

[erdemyerebasmaz]

This PR addresses #132

Initially, I assumed we were not displaying a loader while the fiat currency data is being loaded. However, it seems drag_and_drop_list dependency has a performance issue with displaying large lists which blocks the UI thread.

Since fiat currency data is loaded almost immediately, the UI thread is blocked on the page that's navigating to FiatCurrencySettings until DragAndDropList is ready to display it's items. This behavior hid critical UI feedback, page route animation & loading animation from the user.

An artificial delay of 800ms is added to render page route animation + few spins of loader first before UI thread is blocked as a workaround.

Here's a video showing the UI behavior w/ & w/o the solution:

VN20221006_132406.mp4

[erdemyerebasmaz]

One other suggestion is using DragAndDropList for selected currencies only and ListView for the unselected fiat currencies since we're only using drag & drop operations on selected currencies.

However, it has it's own set of issues:

SVID_20221010_112430_1.mp4

These issues do exist on using a single DragAndDropList but not encountered due to the sheer size of the list.