Resin-sdk

* Add unit test for device class. 82 [Trong Nghia Nguyen]

* Add resin.model.tag.ApplicationTag that implements Application tag model for Resin Python SDK. 80 [Trong Nghia Nguyen]
* Add resin.model.tag.DeviceTag that implements device tag model for Resin Python SDK. 80 [Trong Nghia Nguyen]

* Remove low level class resin.Token since all features are now merged into resin.Auth 79 [Trong Nghia Nguyen]
* Revamp resin.Auth model to work with Auth Token and API token. 79 [Trong Nghia Nguyen]
* Add resin.models.api_key.ApiKey class that implements user API key model for Resin Python SDK. 79 [Trong Nghia Nguyen]

* *BREAKING* Change application.create() to support application types. 76 [Trong Nghia Nguyen]
* *BREAKING* Change device.name to device.device_name everywhere. 76 [Trong Nghia Nguyen]
* *BREAKING* Remove resin.models.build model which is replaced by release model. Remove resin.models.device.set_to_build() function. 76 [Trong Nghia Nguyen]
* Implement resin.models.config_variable.ApplicationConfigVariable model. 76 [Trong Nghia Nguyen]
* Implement resin.models.config_variable.DeviceConfigVariable model. 76 [Trong Nghia Nguyen]
* *BREAKING* Remove resin.models.environment_variables.ApplicationEnvVariable since it no longer exists in the model. Implement resin.models.environment_variables.ServiceEnvVariable model 76 [Trong Nghia Nguyen]
* *BREAKING*: Remove resin.models.DeviceEnvVariable since it no longer exist in the model. Implement resin.models.DeviceServiceEnvVariable model to work with Device Service Variables. 76 [Trong Nghia Nguyen]
* Add resin.models.service model to lookup for services. 76 [Trong Nghia Nguyen]
* Add resin.models.image to look up individual image build. 76 [Trong Nghia Nguyen]
* *Breaking*: Move to API v4 (Multicontainer support). 76 [Trong Nghia Nguyen]

* Fix device.get_status() function, use `last_vpn_event` field instead of `last_seen_time` since it no longer exists. 75 [Trong Nghia Nguyen]
* Fix return object of `create` functions to ensure they return a dict. 75 [Trong Nghia Nguyen]
* Fix resin.models.application.create() return object. 75 [Trong Nghia Nguyen]
* Update device.set_to_build() to work with latest API. Change the argument from build id to build commit hash since build id is not available on the dashboard. 75 [Trong Nghia Nguyen]

* Drop support for Python 2.6 Python 2.6 is pretty old and has been EOL since 2013. It is also not compatible with current test suite. 69 [Trong Nghia Nguyen]
* Properly parse request data before sending. 69 [Trong Nghia Nguyen]
* Add the test suite to Travis. 69 [Trong Nghia Nguyen]
* Ensure the test suite refuses to run with an admin user account. 69 [Trong Nghia Nguyen]
* Implement unit test for application class. 69 [Trong Nghia Nguyen]