Fix the time-oracle scope [ECR-3091] (#823)

time oracle was incorrectly packaged in the QA service
artifact, causing TimeSchemaProxy to be loaded by the classloader
of that service artifact, which cannot link to an already loaded
by the application classloader java_bindings native library.

That's another reason to reconsider https://jira.bf.local/browse/ECR-3046
which would have provided a proper error message earlier.

Also, make isTimeServiceEnabled static as there is no reason
for it to be an instance method (and native already implemented
as for static):

pub extern "system" fn Java_com_exonum_binding_time_TimeSchemaProxy_isTimeServiceEnabled(
    _: JNIEnv,
    _: JClass, // <- !
) -> jboolean {

Author: dmitry-timofeev

exonum-java-binding/qa-service/pom.xml

@@ -38,10 +38,10 @@
       <scope>provided</scope>
     </dependency>
 
-    <!-- Time oracle is a compile-scoped dependency till Packaging is delivered. -->
     <dependency>
       <groupId>com.exonum.binding</groupId>
       <artifactId>exonum-time-oracle</artifactId>
+      <scope>provided</scope>
     </dependency>
 
     <dependency>

exonum-java-binding/time-oracle/README.md

@@ -13,14 +13,15 @@ Include `exonum-time-oracle` as a dependency in your `pom.xml`:
       <groupId>com.exonum.binding</groupId>
       <artifactId>exonum-time-oracle</artifactId>
       <version>0.6.0-SNAPSHOT</version>
+      <scope>provided</scope>
     </dependency>
 ```
 
 To use the time oracle, we should enable it. To do that, include its name `time` in
 `services.toml` configuration file in the Exonum Java app's directory with the following content:
 
 ```toml
-services = ["time"]
+system_services = ["time"]
 ```
 
 See more information on built-in services [here][built-in-services].

exonum-java-binding/time-oracle/src/main/java/com/exonum/binding/time/TimeSchemaProxy.java

@@ -71,7 +71,7 @@ private static boolean runningUnitTests() {
     }
   }
 
-  private native boolean isTimeServiceEnabled();
+  private static native boolean isTimeServiceEnabled();
 
   /**
    * Mapping for Exonum time indexes by name.