Reorder and rename params to TreeView_Detail::load_partitions()

Reorder the parameters into the same order in which they occur in the
row, i.e. Name first, then Mount Point and finally Label.  Rename local
variables in load_partitions(1 param) and parameters of
load_partitions(5 params) prefixing with "show_" to make it clearer the
variables track if that column will be displayed or not.