[change] Send config_modified signal when device templates are changed and config.status is modified

[nemesifier]

I was expecting the config_modified signal to be sent when templates are added, removed or their order is changed from a device but this doesn't seem to happen if config.status is modified.

How to replicate:

• create a few templates
• create a device and a config, edit the config and save, ensure config status is modified
• add a template to a device or remove or change their order

Expected result:

• config_modified signal emitted

Actual result:

• config_modified signal not emitted

Notes:

• emit signal after post_add or post_remove
• ensure signal is not sent twice (if the contents of the config have already been changed, the signal will be sent, so we must ensure it's not sent twice)

[nemesifier]

While working on this I figured out it's not really a bug but it was implemented this way on purpose, so this is a change of behaviour rather than a bugfix, but I think it's important to do it to avoid ambiguities and make the config_modified signal reliable.