One of the four communication methods uses a DAC for analog signal sharing....

One of the four communication methods uses a DAC for analog signal sharing. This commit implements a first non-tested version of this feature.

Four files were modified to implement this feature:
- The low layer dac_configuration.h and .cpp: These files allow access to the dac module and can set any dac to constant value mode. The constant value can also be set.
- The HardwareConfiguration API: They give access to the low-leve configuration file to the user.