ThingsBoard IoT Gateway

Minor release with the following improvements.

Improvements:

• [Connectors] Improvements to RPC requests and attribute update requests processing;
• [TB gateway service] Improvements in configuration processing;
• [Request Connector] Improvements for data processing from external API;
• Code refactor.

Bug fixes:

• [Modbus Connector] Fix for #262;
• [Modbus Connector] Fix for #261;
• [Custom serial connector] Fix for device processing;