add support for button tags

[tschanzt]

@jone this adds support for the button tag. I added a subclass of the default lxml HtmlParser so we can add the tag as a InputElement. Also i changed the function to use our own self.input function since i had to add the buttons there. Therefore the items were now wrapped by ftw.testbrowser.

[tschanzt]

basicly the has the same behaviour as the except that it can hold other elements. lxml creates a InputElement object for all tags but only a general HtmlElement for the elements since our wrapper functions depend on attributes which are only available on the InputElements it was easiest to just create a new one but i lost the context so iterancestors didn't work properly.

So i needed to update the HtmlElementClassLookup object which is created in the init of the Parser and i didn't want to just change it in the default parser since it could affect other application. therefore i added a custom parser. the custom HtmlElementClassLookup is so we can add our button mapping without loosing the default mappings, since the default one does either take the default or a completely new mapping. You cant combine them with the default one.

I hope this makes kind of sense.

[jone]

Thank you for this explenation, now I understand agree to your approach 👍

[tschanzt]

@jone updated.

[tschanzt]

@jone updated

[tschanzt]

@jone i changed the text of the button.