'Initializes the HostsSidebar. Initialization by itself does
almost nothing, the application will inmediatly call create_model
with the last workspace and create_view with that model upon startup.
The model looks like this:
| HOST_ID | HOST_OS_PIXBUF   | OS_STR | DISPLAY_STR      | VULN_COUNT|
| a923fd  | PixBufIcon(linux)| linux  | 192.168.1.2 (5)  |      5    |'

def __init__(self, open_dialog_callback, get_several_hosts_function, get_single_host_function, icons):

    Gtk.Widget.__init__(self)
    self.open_dialog_callback = open_dialog_callback
    self.get_hosts_function = get_several_hosts_function
    self.get_single_host_function = get_single_host_function
    self.model = Gtk.ListStore(str, GdkPixbuf.Pixbuf(), str, str, int)
    self.create_view()
    self.progress_label = Gtk.Label('')
    self.host_amount_total = 0
    self.host_amount_in_model = 0
    self.page = 0
    self.host_id_to_iter = {}
    self.linux_icon = (icons + 'tux.png')
    self.windows_icon = (icons + 'windows.png')
    self.mac_icon = (icons + 'Apple.png')
    self.no_os_icon = (icons + 'TreeHost.png')
