Build: Set javac release property (ticket #2775)

Ant version 1.9.8 or higher now required
Drop support for Xenial package build
Fix up BOB build configuration
Fix i2psnark standalone build

apps/sam/java/build.xml

@@ -25,6 +25,7 @@
     <!-- only used if not set by a higher build.xml -->
     <property name="javac.compilerargs" value="" />
     <property name="javac.version" value="1.8" />
+    <property name="javac.release" value="8" />
     <property name="manifest.classpath.name" value="Class-Path" />
 
     <!-- compile everything including client classes -->
@@ -34,6 +35,7 @@
         <javac 
             srcdir="./src" 
             debug="true" deprecation="on" source="${javac.version}" target="${javac.version}" 
+            release="${javac.release}"
             includeAntRuntime="false"
             encoding="UTF-8"
             destdir="./build/obj" 
@@ -46,6 +48,7 @@
         <javac 
             srcdir="./test" 
             debug="true" deprecation="on" source="${javac.version}" target="${javac.version}"
+            release="${javac.release}"
             includeAntRuntime="false"
             encoding="UTF-8"
             destdir="./build/obj"