Fix namespacing issues for links in render helpers

[shekibobo]

• d3c0e0d removed the ability to use namespaces on the sortable tree helper. This reinstates that capability, but also adds consistent rendering and namespacing for all render helpers.
• ce696f3 meant to clarify that a show link was not being used for a delete link, but neglected to update in all the helpers. This PR also addresses that issue.
• Actually, this PR makes each renderer consistent in how it builds links, and allows you to explicitly pass what controller you want to use for building said links.

[the-teacher]

looks fine - I will try it on my dummy app - if it's works correct - I will be glad to merge it

thank you!

[shekibobo]

Just so you know, I may have one or two more adjustments coming through on separate PRs today. I'm trying to get this working with ActiveAdmin, and there are a few issues I'm working through...

[shekibobo]

Actually, I lied. I'm including that as part of this PR. Instead of trying to infer the link controller from the klass option, we first check to see if the user passed a controller option, and we use that instead.

[shekibobo]

So I'm not sure exactly how this is working, but namespace is never actually used. I have namespaced routes (under /admin using ActiveAdmin), and after removing the namespace option from my tree renderer call, it still works fine. However, my controller is named (without a namespace) to make it work properly, since my class name does not match my controller name.

[shekibobo]

It turns out that adding the namespace options just added the value to the URL query string, which was not what the end goal was.

[the-teacher]

It was good PR. I have to keep it in mind if I will improve the gem.
Thanks again!