Landingpage: Add contact form

[pfecht]

Add the contact form to the landingpage (see the screenshot below, see design in slack channel).

Acceptance Criteria:

• Implement the contact form
  • Use the ino-input and ino-textarea in outlined mode
  • Design guidelines have been followed.
• A dl-elements mailing list has been created
• An email will be send to our Dl-Elements
• The users email client will be opened with prefilled text on submit