Move plugin: Code needs cleanup

Examples:
There are a ton of

if (a)
    if (b)
        if (c)
        {
            do ()
        }

combinations, or things like:

 if (s->otherGrabExist ("move", NULL))
     return false;

 if (ms->w)
     return false;

 if (w->type () & (CompWindowTypeDesktopMask |
         CompWindowTypeDockMask |
         CompWindowTypeFullscreenMask))
     return false;

 if (w->overrideRedirect ())
     return false;

which can be better written as:

 if (s->otherGrabExist ("move", NULL) ||
     ms->w ||
     w->overrideRedirect () ||
     w->type () & (CompWindowTypeDesktopMask |
     CompWindowTypeDockMask |
     CompWindowTypeFullscreenMask))
     return false;

also this block above comes after these lines:

 unsigned int mods = CompOption::getIntOptionNamed (options, "modifiers", 0);

 int x = CompOption::getIntOptionNamed (options, "x", w->geometry ().x () +
            (w->size ().width () / 2));
 int y = CompOption::getIntOptionNamed (options, "y", w->geometry ().y () +
            (w->size ().height () / 2));

 int button = CompOption::getIntOptionNamed (options, "button", -1);

but all those calculations of local variables do not need to happen if we return false, so
those should be calculated after the return false check...