Migrate UI to React

[php-coder]

Most of the forms can be ported to React as they only available to authenticated (and in most cases to a privileged) users. We will get the following benefits:

• features will be decoupled on HTTP level (see also Split packages by features #927, Split code to Maven modules #1002). For example, SeriesController is coupled with country, category, sales, participants and collection only because we need to show this information on series info page. With React, the components will load all required information via HTTP.
• completely removes an issue where we have to invalidate pages of authenticated users as there might be some sensitive data. With React components, the page content is always the same and only some parts are loading when needed. The permitions to load the parts can be constrained by URLs.
• it also helps in introduction of microservices (Split to microservices #1162) as React components will load data via API.

We can't transform it to a fully Single Page Application (SPA) as some pages should be available to search engine bots but all the interactive pages can be partially or fully moved to React.

This task depends on:

• Add series sale form: port to React #1056 Add series sale form: port to React
• Import series sale form: port to React #1057 Import series sale form: port to React
• /series/{id}: rewrite series sales block to React #1329 /series/{id}: rewrite series sales block to React
• Implement API for fetching all sales of a series #1330 Implement API for fetching all sales of a series
• Add React component for country creation #1345 Add React component for country creation
• Implement API for country creation #1347 Implement API for country creation
• Add React component for category creation #1346 Add React component for category creation
• Implement API for category creation #1348 Implement API for category creation
• Use React Hooks instead of classes #1506 Use React Hooks instead of classes
• more tasks are coming