Move php-settings.el to php-mode-init.el

This seems like a better naming scheme to me, mirroring the Emacs naming
scheme as it does.
Use require instead of load-file to load php-mode-init.el

It's more robust against restructuring files.
Move all php-mode config inside the php-mode hook

This may need tweaking, but if I do this sort of thing everywhere,
it should speed up my load times significantly.
Lazy-load PHP mode customizations

If I break enough of my init file out into lazy-loaded chunks, maybe my
boot time will get to something semi-tolerable.