Add integration test for PluginManager

We want to make sure that Plugin Manager still downloading plugins from internet.
New tests requires internet access (`@Network` annotation has been added).

By default, tests annotated with `@Network` are not launched.

If you need to run these tests, use `-Dtests.network=true` option.

Closes #3894.
Support date math for `origin` decay function parsing

The parser used the method that was supposed to be used for parsing on
the indexing side that never supported date math.

Closes #3892