UI: Upgrade stream link hotlink to a button

Most of the top streaming services now have a link in the stream key
label. Upgrading this button to a button clarifies the assistance
for the important step of setting up a stream.

Creates a new type of button for URL opening simply which also
automatically updates the tootip to the current URL.

Includes addition of Twitter/Periscope URL to make this feature more
complete.

UI/url-push-button.cpp

@@ -0,0 +1,26 @@
+#include "url-push-button.hpp"
+
+#include <QUrl>
+#include <QMouseEvent>
+#include <QDesktopServices>
+
+void UrlPushButton::setTargetUrl(QUrl url)
+{
+	setToolTip(url.toString());
+	m_targetUrl = url;
+}
+
+QUrl UrlPushButton::targetUrl()
+{
+	return m_targetUrl;
+}
+
+void UrlPushButton::mousePressEvent(QMouseEvent *event)
+{
+	Q_UNUSED(event)
+	QUrl openUrl = m_targetUrl;
+	if (openUrl.isEmpty())
+		return;
+
+	QDesktopServices::openUrl(openUrl);
+}