Proposal for utf-8 support in sls files

So, this refers to #8947.
On this PR there are tests, but also two core changes:
 - a test on jinja errors treatmments, to fix any unicode characters in the context buffers and push that to utf-8 before outputing
 - a recursive function after yaml stuff to detect any unicode strings and push it to utf-8.

From my tests jinja is always outputing unicode strings from utf-8 inputs and yaml is making any non-ascii string an unicode string. But the whole salt code is only managing ``str`` (utf-8) and not ``unicode`` strings.