Enable and disable logics

[ohinckel]

(copied from mknx/smarthome#137)

In some cases it makes sense to temporarily disable a given logic and enable later again. At least I would like to disable some logics for some days but enable it again later. And I don't want to comment out the logic and restart SmartHome.py.

This patch contains the following enhancements:

• enable and disable logics with logic.enable() and logic.disable()
• check enabled status with logic.enabled property
• enable and disable logic using el and dl CLI commands
• show if logic is disabled when using ll CLI command
• add posibility to enable and disable logics via visu plugin (using { "cmd" : "logic", "name" : "<name>", "enabled" : 0/1 } - the val attribute can also be specified to additionally trigger the logic, as this is the current behaviour)

[psilo909]

will try to review this some day this week, as i highly need that PR for myself

[ohinckel]

Just to quote myself (from the original issue):

I just saw, that the scheduler has already an ˋactiveˋ flag for all tasks. Since each (cron/cycle)
logic is a task in the scheduler we can use this instead of using an own flag in the logic object.

If possible this patch can be changed to retrieve the ˋactiveˋ flag from the scheduler for a
given logic to show it enabled or disabled. The methods to change the flag could simply tell
the scheduler to activate or deactivate the logic task.

But I'm not sure if this is a clean solution. Suggestions and ideas are welcome.

Using the scheduler's active flag instead would completely remove the logic execution/trigger (which would be better since it is not anymore in the task/run queue of the scheduler) but needs more coupling between scheduler and logic class (because enabling/disabling would require a scheduler.change() and retrieval of the active status of a logic access to the schedulers tasks).

The current implementation triggers the logic in any case (enabled or disabled) and will just skip the actual logic execution.

I'm still not sure which is the best implementation. So suggestions are welcome!