Image min/max and higher-precision temperature

A few commits:

* Fixing Alex's image min/max so now it is returned even under most error states
* ImperxStream can now return a higher-precision camera temperature (0.25 degree steps)
* The higher-precision temperature is put into the telemetry packet sent to the GSE using the class Float2B, which compacts a float into 2 bytes.

Of course, without matching code on the GSE, the camera temperature currently looks like garbage.  Once Steve has merged into his submodule the SAS commit with the Float2B code, the uint16_t housekeeping field can be converted back into a float with the following code:

    self.dataPacket.cameraTemperature = Float2B(housekeeping1).value();

Merging immediately