Introduce inital draft of hawkBit SDK (#1638)

Intends to provide a Java SDK facilitating:
* development of back-end integrations using mgmt api (including UI-s)
* development of java based high-end devices (which could run Spring apps) to communicate with hawkBit via DDI API
* implementation of demo/test cases using device & management SDK

Status: initial draft
 - Feign client did & management API - done
 - Hal/HATEAOS Support - works (including in non-web apps)
 - device communication works when no software updates (e.g. pulling software base)
 - demo for single and multiple devices simulation (including management API uses)
 - TODO - fix software update flows
 - TODO - provide more integration points for developers to interact with device SDK

Signed-off-by: Marinov Avgustin <Avgustin.Marinov@bosch.com>

.gitignore

@@ -61,6 +61,7 @@ maven.properties
 
 # Test Files
 *.tmp
+spring-shell.log
 
 # Documentation
 .gitmodules