Add heater control parameters to TunerStudio

[xtitoris]

Moved some heater parameters into config memory.
Specifically

• HeaterSupplyOffVoltage
• HeaterSupplyOnVoltage
• PreheatTimeSec

This way the board could be configured to work independently of the ECU, so that

• Heater only turns on when alternator produces high enough voltage (as an indirect measurement of when engine is running), by setting HeaterSupplyOnVoltage higher than ~13.5V
• And/or increasing PreheatTimeSec to 5-10 minutes to allow engine to warm up a bit, and water condensation to evaporate.

To conserve the precious RAM, ScaledValue struct is introduces, that allows seamlessly mapping int/uint values.
This way values could be mapped to integers, scaling them both up and down.

• Fractional point values, like 12.5 could be mapped to 125 in memory, if more precision is needed.
• Precision can be sacrificed to fit larger values into smaller types. E.g. values from 0 to 1275 can be fitted into uint8_t using steps of 5.

Added unit tests for ScaledValue, so that it definitely fits into its storage type
And unit tests for Configuration, to make sure changes to config structure would be backward-compatible with existing units.

[dron0gus]

Why new class FixedPoint? Why not ScaledChannel?
Does it worth to store PreheatTimeSec in uint8_t with 5 scale? To save 1 byte?

[xtitoris]

Does it worth to store PreheatTimeSec in uint8_t with 5 scale? To save 1 byte?

Well, if we decide to make more timeouts user-configurable, like HEATER_WARMUP_TIMEOUT, HEATER_DIDNOTHEAT_RETRY_TIMEOUT, and others, or add HEATER_FAST_HEATING_THRESHOLD_T to the config, none of which require single digit precision, it would run away quick, with one byte wasted for each of these values.

[xtitoris]

I've also played around with making these values variable bit-width, so that we could store, for example, three uint16_t : 10 values in two bytes, but TunerStudio does not support that.