small init error in Icosphere

Created by: zeffii

@portnov

the node will report a key error, until the user sets the subdivisions slider..

 return self['subdivisions']
KeyError: 'bpy_struct[key]: key "subdivisions" not found'
File "\sverchok\nodes\generator\icosphere.py", line 96, in get_subdivisions

i also had this with the A number node , you have to assign something to the idproperty in the sv_init, so something like

    def sv_init(self):
       ...
       self['subdivisions'] = some_default
       # existing code

see. https://github.com/nortikin/sverchok/blob/master/nodes/number/numbers.py#L80-L84