Added ApiKey/Token authentication

[dstenger]

Enables authentication via X-API-Key when REST interface is used.

[copierrj]

A few small remarks:

• Documentation is missing.
• Having a read-only workspace configuration implicitly disables access to the API.
• ConfigServlet.token is a static field. It should be non static and initialized in the init method.

[stephanr]

In addition, there is the question of how this should be handled in the context of the existing protection for deegree rest-api.

deegree3/deegree-services/deegree-webservices/src/main/webapp/WEB-INF/web.xml

Lines 78 to 96 in 92ac14c

	<security-constraint>
	<web-resource-collection>
	<web-resource-name>Configuration</web-resource-name>
	<url-pattern>/config/*</url-pattern>
	</web-resource-collection>
	<auth-constraint>
	<role-name>deegree</role-name>
	</auth-constraint>
	</security-constraint>
	<login-config>
	<auth-method>BASIC</auth-method>
	<realm-name>deegree web configuration API</realm-name>
	</login-config>
	<security-role>
	<description>deegree administrator role</description>
	<role-name>deegree</role-name>
	</security-role>

[stephanr]

I am closing this in favor of the reworked #1498