Allow to publish data as float, int, uint

[IzabellaRaulin]

Support of publishing data as a string (default) but also as a float, int or uint (configurable in task manifest) because of processing this data after they are stored in postgresql db (or even display them as a graph).

If user set in task manifest that data will be published as an uint, but incoming data cannot be parsed to this type, warning or error will occures

• when incoming data cannot be converted to expected format, returns error
• when incoming data could be converted to expected format but part of data will be lost, logs about it

Publish data as a string should be default because it a) works for all incoming data types, b) maintains current behavior.

Feel free to comment this proposition.