Add UI for showing todo items of a series

[php-coder]

On the src/main/webapp/WEB-INF/views/series/info.html page we should show a list of todo items. It should have a header "TODO" (see "Similar series" as example). Every item should be a checkbox.

The items should be loaded from API (/todo/items?series_id=ID) and they might look like the following:

[
  {1, "Replace an image"},
  {2, "Add Michel numbers"}
]

In case of a failure from a server, the error should be shown.

Part of #197

[php-coder]

@milik27 Hi, please, let me know whether you still want to work on this issue. Otherwise, I'll assign it to another person. Thanks!