all: Refactor to nonglobal Viper, i18n etc.

This is a final rewrite that removes all the global state in Hugo, which also enables
the use if `t.Parallel` in tests.

Updates #2701
Fixes #3016

hugolib/shortcodeparser_test.go

@@ -152,6 +152,7 @@ var shortCodeLexerTests = []shortCodeLexerTest{
 }
 
 func TestShortcodeLexer(t *testing.T) {
+	t.Parallel()
 	for i, test := range shortCodeLexerTests {
 		items := collect(&test)
 		if !equal(items, test.items) {