LibCore: Put all classes in the Core namespace and remove the leading C

I've been wanting to do this for a long time. It's time we start being
consistent about how this stuff works.

The new convention is:

- "LibFoo" is a userspace library that provides the "Foo" namespace.

That's it :^) This was pretty tedious to convert and I didn't even
start on LibGUI yet. But it's coming up next.

Applications/ChanViewer/BoardListModel.cpp

@@ -44,7 +44,7 @@ BoardListModel::~BoardListModel()
 
 void BoardListModel::update()
 {
-    CHttpRequest request;
+    Core::HttpRequest request;
     request.set_url("http://a.4cdn.org/boards.json");
 
     if (m_pending_job)

Applications/ChanViewer/BoardListModel.h

@@ -51,5 +51,5 @@ private:
     BoardListModel();
 
     JsonArray m_boards;
-    RefPtr<CHttpJob> m_pending_job;
+    RefPtr<Core::HttpJob> m_pending_job;
 };

Applications/ChanViewer/ThreadCatalogModel.cpp

@@ -52,7 +52,7 @@ void ThreadCatalogModel::set_board(const String& board)
 
 void ThreadCatalogModel::update()
 {
-    CHttpRequest request;
+    Core::HttpRequest request;
     request.set_url(String::format("http://a.4cdn.org/%s/catalog.json", m_board.characters()));
 
     if (m_pending_job)

Applications/ChanViewer/ThreadCatalogModel.h

@@ -63,5 +63,5 @@ private:
 
     String m_board { "g" };
     JsonArray m_catalog;
-    RefPtr<CHttpJob> m_pending_job;
+    RefPtr<Core::HttpJob> m_pending_job;
 };