#69 separate block for autogenerated code

[Alex]

When Boa generate code in wxPython, it mark all function is auto-generated and do not edit it.
I offer all autogenerated code place into comment block like this:

## Boa:autogenerated:start
...
## Boa:autogenerated:end

and allow manual edit function outside this block, delete function only if no manual edited code is added, else show warning.