Update data format to support composite entities

[tabergma]

Description of Problem:
In a sentence like I want to fly from Berlin to Amsterdam. we not only want to annotate Berlin and Amsterdam as entities city, but also want to assign specific roles to them. Berlin should have the role origin and Amsterdam should have the role destination. With the current data format this is not doable.

Overview of the Solution:
Markdown
We want to change the annotation format for entities:
I want to fly from [Berlin]{"entity": "city", "role": "origin"} to [LA]{"entity": "city", "role": "destination", "value": "Los Angeles"}. or
Show me [red]{"entity": "colour", "group": 0} [balloons]{"entity": "item", "group": 0} and [black]{"entity": "colour", "group": 1} [shoes]{"entity": "item", "group": 1}.

We will use {} to define entities that have roles/groups/synonyms. If you just have a simple entity without any role/group/synonym, the old format can still be used ([Berlin](city)).
We will deprecate the old syntax for synonyms, e.g. [LA](city:Los Angeles). Instead users should use [LA]{"entity": "city", "value": "Los Angeles"}. We should offer a script that converts the old format into the new format.

JSON
We simply add new keywords to the entity definition in the JSON format:

{
    "intent": "fly",
    "entities": [
        {
            "start": 19,
            "end": 25,
            "value": "Berlin",
            "entity": "city",
            "role": "from",          
        },
        {
            "start": 29,
            "end": 31,
            "value": "Los Angeles",
            "entity": "city",
            "role": "to",          
        }
    ],
    "text": "I want to fly from Berlin to LA."
},

Definition of Done:

• Tests are added
• New training data format is supported
• We have a script in place that converts the old format to the new format
• Documentation
• Changelog

[erohmensing]

@tabergma would there be a big argument for keeping in-line synonyms and not deprecating that completely? i.e. just leaving the separate

synonym:Los Angeles
- LA

format?

[tabergma]

No reason to remove this. We can keep this.