group module: configurable orientation

[baodrate]

currently, the orientation of group modules is always the opposite of the bar. Change it so that:

• the default orientation of the group module is always the opposite of its parent, even for nested groups
• the orientation can be overridden in the config
• css ID and class are set for the group element

Motivation:

I would like to set styling for sets of modules so that they are visually grouped. Some of this can be simulated by enumerating style settings for each module, but many things are not possible when all the modules' elements are siblings of each other

The module group functionality is a bit is a bit inflexible and only really viable for a specific use case. This hopefully makes it more generally useful