Mapping Support

[raffael0]

Create a mapping.toml schema that can specify for each field:

• name mapping
• mapped value (from raw value with slope and offset)
• logical value (from mapped value with a list of expressions, where the first match defines the value), possibly with some color code / warning level

all names in the mapping must be unique.

also add support in the NodeManager for reading/writing values, taking into account the mapping