Check duplicities in attribute names

[dmoranj]

Currently, the IoT Agent doesn't make any duplicity checks on the names that are provisioned via the Device Provisioning API or the Configuration API. The following checks should be done in each incoming creation or update:

• In a Device provisioning, each attribute name in the active, lazy, static or command category arrays must be unique among all the categories.
• In a Configuration provisioning, each attribute name in the active, lazy, static or command category arrays must be unique among all the categories.
• If a Device belonging to a Configuration is provisioned, and an attribute in any of the attribute categories (e.g: lazy) is defined in that provision, its name should not be present in any other category (e.g: active or command). I.e: a lazy attribute in the device should be able to overwrite a lazy attribute in the Configuration, but should not conflict with attributes in the active, command or static categories.