Bug : for DDC devices, the status returned an error "Invalid staus string", now fixed.

Tango_OMemstream removed, string used instead

- DDC status show only errors if any
- added command to get DDC model configuration

- minor change (std::cout removed)

- SRQ management changed :
* ReadStatusByteRegister method added
* IsSrqLineUP added

- Integration Mode available for DDC/SCPI devices
- tests done with a K617 (DDC) and a K6485 (SCPI)

- integration mode OK (tests done with K_486)

- TODO: DDC/SCPI
integration time for ScanServer compatibility.
report config for all DDC
add configuration in SCPI start command

- trigger mode and buffer size management added.
- TODO: DDC/SCPI
integration time for ScanServer compatibility.
SRQ management for Keithley Integration mode