protecting against UnicodeDecodeError in yaml dump

yaml.dump()  was dying  with UnicodeDecodeError  when trying to
 serialize a python object which contained a string that was not in a in utf8
Revert "protecting against UnicodeDecodeError in yaml dump"

This reverts commit cdbe341eb3abd24556a229a5a40312b95509ad54.
Improving yaml_literal presenter. Allan's implementation
adding back a line removed by mistake
replacing yaml_literal with the new utility funciton yaml_dump. removing other unused import
replace yaml.dump with new dump_yaml wrapper
Merge remote-tracking branch 'fede/fix_utf8' into 2.0

Conflicts:
	src/rez/resolved_context.py
	src/rez/util.py