Error handling for server calls

[ryukzak]

Right now, usually, in case of a network error, we use console.log() or (which is better) alert(). We need to fix this:

• show all error to a user;
• show it in a nice and usable way (e.g., classical temporary red panel on top of the screen).

How to reproduce:

• run UI by yarn start;
• run the NITTA server;
• do something and halt the server;
• do something which requires access to the server.

An error message should be helpful. For example, we can include expecting server port.

[iburakov]

RequestResult utility component (components/utils/RequestResult) can be used to conveniently

1. display spinner when loading
2. display error message with refresh button (default) or customized content on error
3. render result on success

See usage for examples.