Fix: signal/slot macro -> func pointer & network fixes

- convert qt connect calls to use function pointers instead of the signal/slot macros wherever practical (UI classes were mostly left alone, target was tasks and processes)
- give signals an explicit receivers to use the static method over the instance method wherever practical
- ensure networks tasks are using the `errorOccured` signal added in Qt5.15 over the deprecated `error` signal
- ensure all networks tasks have an sslErrors signal connected
- add seemingly missing `MinecraftAccount::authSucceeded` connection for `MSAInteractive` login flow

Signed-off-by: Rachel Powers <508861+Ryex@users.noreply.github.com>

launcher/net/HttpMetaCache.cpp

@@ -55,7 +55,7 @@ HttpMetaCache::HttpMetaCache(QString path) : QObject(), m_index_file(path)
     saveBatchingTimer.setSingleShot(true);
     saveBatchingTimer.setTimerType(Qt::VeryCoarseTimer);
 
-    connect(&saveBatchingTimer, SIGNAL(timeout()), SLOT(SaveNow()));
+    connect(&saveBatchingTimer, &QTimer::timeout, this, &HttpMetaCache::SaveNow);
 }
 
 HttpMetaCache::~HttpMetaCache()