State changed events for Actuators

[s-kostyuk]

Implement a some sort of events from C#, add events like 'on_state_changed' to the base implementation of Actuator

[s-kostyuk]

It's implemented in the experimental branch. But here are the issues:

• all implementations of Thing and derived classes must to watch their changes manually;
• i.e. that means that an integration creator is obliged to watch which properties will be affected by an execution of each of the Thing's methods, manually capture the old and the new values of the property and manually call on_property_changed callback;
• ... and such situations sucks;
• here is an another issue: inconsistency;
• for now Services implement an Observable-style notifications and Things implement OnPropertyChanged-style notifications;
• so we have two different approaches used for notifications in the system;
• that sucks too.

[s-kostyuk]

Although an experimental implementation of on_propety_changed is available in experimental branch and is likely to be merged to devel before v0.3, this issue will be postponed to the next release until the mentioned issues will be resolved

[s-kostyuk]

Well, after some consideration, it was decided to simplify things greatly. All the Things will generate only "object_changed" events or something in this manner. Information about what exactly was changed in the Thing will be omitted for now (until will this functionality will be specifically requested by another developers or will become urgent for implementation of a new functionality).