Bump java language to 11 (#980)

* Moved java XML and annotations dependencies to project level instead
of as profiles
* Set compiler language level to 11
* Removed jdk8 from travis build

* Kept java level 8 in naked-objects/dom for datanucleus enhancer, for
now.

naked-objects/dom/pom.xml

@@ -36,6 +36,17 @@
 				</excludes>
 			</resource>
 		</resources>
+		<plugins>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-compiler-plugin</artifactId>
+				<version>${compiler.version}</version>
+				<configuration>
+					<source>8</source>
+					<target>8</target>
+				</configuration>
+			</plugin>
+		</plugins>
 	</build>
 
 	<dependencies>