Enable & disable technologies

[GrbavaCigla]

There doesn't seem to be any disable/enable technology implementation.

[jmagnuson]

Thanks! It looks like the intent is to modify the Powered property for enabling/disabling technologies. connmanctl does similarly in cmd_enable(). But it definitely would be a useful API to have here-- I could see Technology::enable/disable working, since it would already be guaranteed to exist via Manager::get_technologies. The only question (which applies to all properties) is how to handle updating the stale state of the existing Technology instance.