Implemented basic Price FieldType.

> Part of [EZP-23034](https://jira.ez.no/browse/EZP-23034)

## Solved use-cases
Simple prices without any kind VAT of conversion.

## Synopsis
### Value
It has two properties: `(float)$price` and `(bool)$isVatIncluded`.
It accepts as input either a float + a boolean, or a hash with the properties as keys.

### Type
`fromHash()` and `toHash()` are simple dumps or the value's properties.
`acceptValue()` accepts a float as the price

### Converter
Maps `data_float` to `price`.
`data_text` is split on comma if not empty, and the first item is set to `isVatIncluded`. The second item, `vatId` is ignored

### Testing
Unit & SPI tests. No API tests yet.

## Follow-up
Manual VAT handling is being worked on in #17. It will be provided via dedicated services with persistence layer implementation.
I guess not :-)