[FEATURE] Future design of the PlantUML Server

A new map feature to retrieve the image map of a diagram is added
[FEATURE] Stub implementation of the new map service
[TASK] Refactoring of the TestUtils class

tryGetResponse method deleted
Compressed diagram strings added as constant strings
[FEATURE] First implementation of the map feature unit test
[TASK] Refactoring, decoding feature is now in a utility class
[FEATURE] Design evolution of the map service

Map implementation is still an empty stub
[FEATURE] Map service totally implemented
[FEATURE] Map usage integrated in the interactive servlet

JSTL (without EL) added
[TASK] SourceInformation replaced by PlantumlUtils

a more complete implementation
[TASK] Add a test about Unicode preservation
[BUGFIX] Text/plain outputs always in unicode