Kernel+ProcessManager: Let processes have an icon and show it in the table.

Processes can now have an icon assigned, which is essentially a 16x16 RGBA32
bitmap exposed as a shared buffer ID.

You set the icon ID by calling set_process_icon(int) and the icon ID will be
exposed through /proc/all.

To make this work, I added a mechanism for making shared buffers globally
accessible. For safety reasons, each app seals the icon buffer before making
it global.

Right now the first call to GWindow::set_icon() is what determines the
process icon. We'll probably change this in the future. :^)

Libraries/LibCore/CProcessStatisticsReader.cpp

@@ -43,6 +43,7 @@ HashMap<pid_t, CProcessStatistics> CProcessStatisticsReader::get_all()
         process.ticks = process_object.get("ticks").to_u32();
         process.priority = process_object.get("priority").to_string();
         process.syscall_count = process_object.get("syscall_count").to_u32();
+        process.icon_id = process_object.get("icon_id").to_int();
 
         // and synthetic data last
         process.username = username_from_uid(process.uid);