Minor web GUI tweaks

[prihoda]

Tweak the web GUI appearance:

• Make input text field full-width
• Add user and bot images
• Make generic templates individually scrollable
• Make chat more narrow (~80% of screen in the middle)
• (?) Add big Get Started button like in Messenger & Telegram, send bot intro message afterwards
• (?) When user sends a message, append it immediately to the chat window, do not wait for server response
• (?) Add typing animation when waiting for bot server response

[mzilinec]

User and bot images can be set in GOLEM_CONFIG

[mzilinec]

Input bar fixed to the bottom.
Fonts and colors changed.

Also to do: template buttons, postbacks

[mzilinec]

Templates, buttons, replies, postbacks: should be working.
Input text: Full width, needs styling.
To do: scrolling, images, typing, get started, websocket/updating.