Support manipulating hierarchical labels

[heyitscassio]

Tested using

from skip import Schematic

sch = Schematic('schematic.kicad_sch')

for glabel in sch.global_label:
    hlabel = sch.hierarchical_label.new()
    hlabel.value = glabel.value
    hlabel.move(glabel.at[0], glabel.at[1], glabel.at[2])
    hlabel.effects.justify.value = glabel.effects.justify.value
    glabel.delete()

sch.write('/tmp/schematic.kicad_sch')