Updown service

[ibaiape]

Added optional generic service for component shutdown/power up called UpDown with the following content:

bool power_on # whether the device should be powered on or not
---
bool result # whether the order was successfully carried out or not
string error_message # text message describing issues when carrying out the power on/off order

Feedback on the service naming is appreciated, as:

• We already have a Power generic interface (even if it's a message) so something like powering could be even more confusing than UpDown (my opinion)
• PowerUp/PowerOff/Shutdown etc. are specific to either setting it on or off

Restructured the generic interfaces' model folders to homogenize with the rest of models.

Separated into a file (generic.xml) containing all generic interfaces for generation and another (base.xml) to group the generic mandatory interfaces (like before).

[ahcorde]

I don't really like the service name UpDown, it's rather confusing.

I would suggest something like:

• turn_on_off
• shutdown
• power_off

@ibaiape, @carlossvg, @igorrecioh suggestions are wellcome.

[igorrecioh]

I have a doubt, the idea of this service is only for switching the component off or also for turning it on? If its aim is to switch off, I would choose Shutdown