Implemented LWJGL version lists.

The LWJGL list actually doesn't use tasks for loading. Instead, it takes advantage of the
QNetworkAccessManager's asynchronous requests. This is a system that I may look to implement for other version
lists and things such as the Minecraft version list and possibly even instance mod lists.

Loading things this way means that code that wants to load a list can simply call the load list function, rather
than having to get a task from the list and execute the task. Unfortunately, it also means we can't have task
progress dialogs for loading lists, but it shouldn't really be too difficult to write one that works with this
system.

At some point in the future, I'll probably end up putting all the code for this method of loading lists into a
base class and then update the other lists to support it.

CMakeLists.txt

@@ -173,6 +173,7 @@ gui/consolewindow.h
 gui/instancemodel.h
 gui/instancedelegate.h
 gui/versionselectdialog.h
+gui/lwjglselectdialog.h
 gui/iconcache.h
 
 multimc_pragma.h
@@ -203,6 +204,7 @@ gui/consolewindow.cpp
 gui/instancemodel.cpp
 gui/instancedelegate.cpp
 gui/versionselectdialog.cpp
+gui/lwjglselectdialog.cpp
 gui/iconcache.cpp
 
 java/javautils.cpp
@@ -222,6 +224,7 @@ gui/browserdialog.ui
 gui/aboutdialog.ui
 gui/consolewindow.ui
 gui/versionselectdialog.ui
+gui/lwjglselectdialog.ui
 )