api: make it possible to hide disabled services in the mux/service grids

This can be done in 3 ways:

none: don't hide anything
all: hide all disabled elements (you can't re-enable in this state)
default: hide those elements whose parents are disabled
webui: minor improvement to service mapping button
webui: minor clean up of toolbar (in services panel)
webui: add support for hidemode in grids. Also tidied a few things up.