theme: use max_toggled_hover.xbm

theme: use max_toggled_hover.xbm

...and treat max_hover_toggled.xbm as an alternative name supported for
compatibility reasons.

Use the following button filename schema: "BUTTON [TOGGLED] [STATE]"
with the words separted by underscore and with the following meaning:
  - BUTTON can be one of 'max', 'iconify', 'close', 'menu'
  - TOGGLED is either 'toggled' or nothing
  - STATE is 'hover' or nothing.

This is consistent with the openbox.org wiki and it is believed that this
is how the vast majority of extant openbox themes out there are written.

But please be aware that it is actually different to vanilla Openbox which
uses: "BUTTON [STATE] [TOGGLED]" following a commit in 2014 which broke
themes and led to some distros patching Openbox:
https://github.com/danakj/openbox/commit/35e92e4c2a45b28d5c2c9b44b64aeb4222098c94

Arch Linux and Debian patch Openbox to keep the old syntax (the one that
this commit aligns us with).
https://gitlab.archlinux.org/archlinux/packaging/packages/openbox/-/blob/main/debian-887908.patch?ref_type=heads