Implement changing update channels

Allow the user to select which update channel they would like to
download updates from.

logic/updater/UpdateChecker.cpp

@@ -24,6 +24,8 @@
 #include <QJsonArray>
 #include <QJsonValue>
 
+#include <settingsobject.h>
+
 #define API_VERSION 0
 #define CHANLIST_FORMAT 0
 
@@ -70,9 +72,8 @@ void UpdateChecker::checkForUpdate(bool notifyNoUpdate)
 
 	m_updateChecking = true;
 
-	// Get the URL for the channel we're using.
-	// TODO: Allow user to select channels. For now, we'll just use the current channel.
-	QString updateChannel = m_currentChannel;
+	// Get the channel we're checking.
+	QString updateChannel = MMC->settings()->get("UpdateChannel").toString();
 
 	// Find the desired channel within the channel list and get its repo URL. If if cannot be
 	// found, error.

logic/updater/UpdateChecker.h

@@ -54,7 +54,7 @@ public:
 	QList<ChannelListEntry> getChannelList() const;
 
 	/*!
-	 * Returns true if the channel list is empty.
+	 * Returns false if the channel list is empty.
 	 */
 	bool hasChannels() const;