Ability to pass additional properties to regular messages

[bezumkin]

After this PR you could send messages with attachments (and interactive buttons) without creating incoming hooks:

props = {
    'attachments': [{
        'fallback': 'Fallback text',
        'author_name': 'Author',
        'author_link': 'http://github.com',
        'text': 'Some text here ...',
        'color': '#59afe1',
        'actions': [{
            'name': 'Interactive button',
            'type': 'button',
            'integration': {}
        }]
    }]
}

message.reply('', props=props)