Re-organize proto directory structure. (#103)

build.gradle and BUILD.bazel/WORKSPACE should not be under the same
directory, since they expect different directory layout for proto files.

.travis.yml

@@ -41,6 +41,7 @@ install:
 script:
   - case "$BUILD" in
       "BAZEL")
+        cd src;
         bazel build --show_result=100 ... ;;
       "MVN")
         mvn verify ;;

build.gradle

@@ -23,10 +23,7 @@ buildscript {
 sourceSets {
     main {
         proto {
-            // In addition to the default 'src/main/proto'
-            srcDir 'opencensus/proto/stats'
-            srcDir 'opencensus/proto/metrics'
-            srcDir 'opencensus/proto/trace'
+            srcDir "src"
         }
     }
 }

pom.xml

@@ -52,11 +52,11 @@
           <pluginArtifact>io.grpc:protoc-gen-grpc-java:${grpc.version}:exe:${os.detected.classifier}</pluginArtifact>
           <protoSourceRoot>.</protoSourceRoot>
 	        <includes>
-            <include>opencensus/proto/agent/*.proto</include>
-            <include>opencensus/proto/exporter/*.proto</include>
-            <include>opencensus/proto/stats/*.proto</include>
-            <include>opencensus/proto/metrics/*.proto</include>
-            <include>opencensus/proto/trace/*.proto</include>
+            <include>src/opencensus/proto/agent/*.proto</include>
+            <include>src/opencensus/proto/exporter/*.proto</include>
+            <include>src/opencensus/proto/stats/*.proto</include>
+            <include>src/opencensus/proto/metrics/*.proto</include>
+            <include>src/opencensus/proto/trace/*.proto</include>
 	        </includes>
         </configuration>
         <executions>