Unify build properties.

- Switch all system properties to project properties.
- Use the ``javaLocalNamingStyle`` instead of the
  ``dot.delimited.style`` for property names, so that it can be directly
  referenced by ``rootProject.propertyName``.
- Recommend users to put GRPC-specific properties in project-level
  ``build.properties`` instead of the user-level.
diff --git a/settings.gradle b/settings.gradle
index fbc6541..be6bdca 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -25,9 +25,8 @@
 project(':grpc-benchmarks').projectDir = "$rootDir/benchmarks" as File
 project(':grpc-examples').projectDir = "$rootDir/examples" as File
 
-if (settings.hasProperty('grpc.skip.codegen')
-    && settings.getProperty('grpc.skip.codegen').toBoolean()) {
-  println '*** Skipping the build of codegen and compilation of proto files because grpc.skip.codegen=true'
+if (settings.hasProperty('skipCodegen') && skipCodegen.toBoolean()) {
+  println '*** Skipping the build of codegen and compilation of proto files because skipCodegen=true'
 } else {
   include ":grpc-compiler"
   project(':grpc-compiler').projectDir = "$rootDir/compiler" as File