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. :^)

Kernel/Syscall.cpp

@@ -299,6 +299,10 @@ static u32 handle(RegisterDump& regs, u32 function, u32 arg1, u32 arg2, u32 arg3
         return current->process().sys$dump_backtrace();
     case Syscall::SC_watch_file:
         return current->process().sys$watch_file((const char*)arg1, (int)arg2);
+    case Syscall::SC_share_buffer_globally:
+        return current->process().sys$share_buffer_globally((int)arg1);
+    case Syscall::SC_set_process_icon:
+        return current->process().sys$set_process_icon((int)arg1);
     default:
         kprintf("<%u> int0x82: Unknown function %u requested {%x, %x, %x}\n", current->process().pid(), function, arg1, arg2, arg3);
         return -ENOSYS;