Add info button even for groups (in LayerSwitcher)

[jacobwod]

Background

Currently layers and group layers can have an optional info button visible next to its' name:

Upon click, this info button expands some informational text about the layer/layer group:

Feature request

Users (and admins) have requested that this info button (with corresponding expandable text area) is also available for pure groups (such as Bygga, Bo & Miljö, in the examples above).