Redesign livechat window on mobile device

[0ndifined]

As a livechat user, I want a mobile friendly, whatsapp-like design for the chat so it's easy for me to read the conversation on a small mobile screen.

Acceptance criteria are:

• send button should be bigger
• font size in general should be 20-40% bigger
• input text field should be bigger

This issue only concerns the full screen livechat window of rocketchat on a mobile device.