Add support for having multiple value providers

[soen]

Do you want to request a feature or report a bug?

Feature.

What is the current behavior?

It is only possible to have a single value provider for all parts of the search query.

What is the expected behavior?

Search query rule elements should be able to specify their value provider through configuration.

What is the motivation / use case for changing the behavior?

Looking the the value providers, Conjunction ships with a built-in one, that allows grabbing dynamic provided values from, say, the query string. However, it was originally designed such that the value provider could be anything really - a web service, the data exchange framework, or such. But one thing that I didn’t plan for, was the need for having more than more source of value provider, and this is something that would be great to extend as well. Imagine that we had some parts of the query that allowed retrieving their values from the query string, then some other parts would grab their values from the data exchange framework, or something else. That way we can truly leverage the power of combining multiple data sources together with searching.

Which versions of Conjunction is affected by this issue? Did this work in previous versions of Conjunction?

Initial version, v1.0.

Other information (e.g. stacktraces, related issues, suggestions how to fix)

N/A