This commit changes the features-tables:
- drop columns 'strategy' and 'parameters'
- add column 'strategies' of type json.
- migrates existing strategy-mappings in to the new format.
The idea is that the 'strategies' column should contain a json-array
of strategy-configuration for the toggle:
```
[{
"name" : "strategy1",
"parameters": { "name": "vale" }
}]
```
To make sure to not break exiting clients the api is extended with a
mapping layer (adding old fields to the json-respons, and mapping
to the new format on create/update a feature toggle.
this commit is first step in solving #102
