Refactoring for Things

[s-kostyuk]

This pull request contains a lot of changes (including BREAKING changes) for the current structure and naming of Things-related components:

• all abstract implementations of Thing and derivative classes are now moved to dpl.integrations package;
• all abstract implementations of Thing and derivative classes now have the Abs prefix in their names;
• Thing class definition is remained unchanged (but there was an idea to rename it to the BaseThing);
• Thing base class now handles the saving of con_instance and con_params constructor params by itself;
• fixed a DTO construction for non-Actuator Things;
• UnsupportedCommandError and UnacceptableCommandArgumentsError exceptions are now defined in things.capabilities.i_actuator module;
• a lot of small PEP8 fixes (mostly for "line too long" errors).