Rename extension instance 'wxHMI' to 'wxglade_hmi'

It is necessary because of following commit 7f59aa398669 ('WxGlade HMI extension now does
only instanciate wx object who's name match extension's name. If no
object match the name and no code is provided in 'start' user python
code section, then a warning is issued')

from __future__ import absolute_import

from etherlab.etherlab import *
from util.BitmapLibrary import AddBitmapFolder
import util.paths as paths

AddBitmapFolder(os.path.join(paths.AbsDir(__file__), "images"))