add emoji auto completion (suggestion)

- typing `<:` will start the emoji auto complition inside the plantuml editor
- for the sake of simplicity the emoji preview of the completion documentation will fetch the image from the original github repository (not plantuml). The reason is that the images (SVGs) inside plantuml have sometimes removed their svg tag, hence it's difficult to set the correct rendering size.
- expand auto completion (suggestion) documentation by default
- add emoji example GIF and documentation
- set charset to utf-8 for each website
- refactor JSON creation inside UI Helper

docs/WebUI/language-features.md

@@ -6,13 +6,23 @@
 
 - type `<&` to get a list of PlantUML available icons
 - see a preview of the suggested icon in its description
+- [PlantUML documentation](https://plantuml.com/openiconic)
 
 ![icons](https://raw.githubusercontent.com/plantuml/plantuml-server/master/docs/WebUI/gifs/auto-completion-icons.gif)
 
+### Emojis
+
+- type `<:` to get a list of PlantUML available icons
+- see a preview of the suggested icon in its description
+- [PlantUML documentation](https://plantuml.com/creole#68305e25f5788db0)
+
+![emojis](https://raw.githubusercontent.com/plantuml/plantuml-server/master/docs/WebUI/gifs/auto-completion-emojis.gif)
+
 ### Themes
 
 - type `!t` to get the suggestion `theme`
 - type `!theme ` to get a list of (local) available PlantUML themes.
+- [PlantUML documentation](https://plantuml.com/theme)
 
 ![themes](https://raw.githubusercontent.com/plantuml/plantuml-server/master/docs/WebUI/gifs/auto-completion-themes.gif)