Add somewhat better blockquote styling

Quotes are now "quoted" and also have a different background.

src/qml/RichLabel.qml

@@ -67,6 +67,18 @@ table td {
     border: 1px solid black;
     padding: 3px;
 }
+blockquote {
+    margin: 0;
+}
+blockquote table {
+    width: 100%;
+    border-width: 0;
+    background-color:" + Kirigami.Theme.alternateBackgroundColor + ";
+}
+blockquote td {
+    width: 100%;
+    padding: " + Kirigami.Units.largeSpacing + ";
+}
 pre {
     white-space: pre-wrap
 }

src/texthandler.cpp

@@ -134,6 +134,10 @@ QString TextHandler::handleRecieveRichText(Qt::TextFormat inputFormat, const Neo
         nextTokenType();
     }
 
+    // Apply user style to blockquotes
+    // Unfortunately some attributes can be only be used on table cells, so we need to wrap the content in one.
+    outputString.replace(TextRegex::blockQuote, QStringLiteral(R"(<blockquote><table><tr><td>“\1”</td></tr></table></blockquote>)"));
+
     // If the message is an emote add the user pill to the front of the message.
     if (event != nullptr) {
         auto e = eventCast<const Quotient::RoomMessageEvent>(event);

src/texthandler.h

@@ -19,6 +19,8 @@ static const QRegularExpression removeReply{QStringLiteral("> <.*?>.*?\\n\\n"),
 static const QRegularExpression removeRichReply{QStringLiteral("<mx-reply>.*?</mx-reply>"), QRegularExpression::DotMatchesEverythingOption};
 static const QRegularExpression codePill{QStringLiteral("<pre><code[^>]*>(.*?)</code></pre>"), QRegularExpression::DotMatchesEverythingOption};
 static const QRegularExpression userPill{QStringLiteral("(<a href=\"https://matrix.to/#/@.*?:.*?\">.*?</a>)"), QRegularExpression::DotMatchesEverythingOption};
+static const QRegularExpression blockQuote{QStringLiteral("<blockquote>\n?(?:<p>)?(.*?)(?:</p>)?\n?</blockquote>"),
+                                           QRegularExpression::DotMatchesEverythingOption};
 static const QRegularExpression strikethrough{QStringLiteral("<del>(.*?)</del>"), QRegularExpression::DotMatchesEverythingOption};
 static const QRegularExpression mxcImage{QStringLiteral(R"AAA(<img(.*?)src="mxc:\/\/(.*?)\/(.*?)"(.*?)>)AAA")};
 static const QRegularExpression plainUrl(