Better reporting for rendering errors + jinja render error fix

In #8364, I made some changes that improve reporting on YAML rendering errors. To do this, I created a new exception class. I found later that there was a similarly-named exception already being used elsewhere in the codebase, so this pull req does the following:

1. Merges the ``SaltRenderError`` and ``RenderError`` exceptions.
2. Fixes all refs to the old RenderError exception that I created in #8364.
3. Fixes #8418, thereby reporting the correct line for jinja render errors. See https://github.com/saltstack/salt/issues/8418#issuecomment-28277788 for more information.

Pending discussion, this should be good to merge.