FEAT(client,markdown): Support multiple code-blocks per message

The way code-blocks are handled was here changed to support multiple code-blocks per message.

This allows content that is not formatted as code between code-blocks, whereas previously everything between the first start of a code-block and the last end of a code-block would become part of one code-block. The only other change is to only end a code-block on the end-signature when it is right after a new line, so triple backticks may also be included as long as they are not at the start of a line.

For explanation on how the regex functions, see [perl - Regex to match any character including new lines](https://stackoverflow.com/a/8303507)

src/mumble/Markdown.cpp

@@ -257,7 +257,7 @@ bool processMarkdownInlineCode(QString &str, qsizetype &offset) {
 bool processMarkdownCodeBlock(QString &str, qsizetype &offset) {
 	// Code blocks are marked as ```code```
 	// Also consume a potential following newline as the <pre> tag will cause a linebreak anyways
-	static const QRegularExpression s_regex(QLatin1String("```.*\\n((?:[^`]|``?[^`]?)*)```(\\r\\n|\\n|\\r)?"));
+	static const QRegularExpression s_regex(QLatin1String("```.*\\n((.|\\n)+?)\\n```(\\r\\n|\\n|\\r)?"));
 
 	const QRegularExpressionMatch match = regexMatch(s_regex, str, offset);
 	if (match.hasMatch()) {