'Gets the output of each extensions.
Merges them in a list and returns it.
:param self: An ExtensionManager object
:type self: ExtensionManager
:return: None
:rtype: None'

def get_output(self):

    output = []
    for extension in self._extensions:
        m_output = extension.send_output()
        num_of_lines = len(m_output)
        if (m_output and (num_of_lines > 0)):
            output += m_output
    return output
