Refactor mantis-publish-netty 3rd party dependency specifications

first pass at refactor 3rd party dependency specifications for mantis-publish-netty and corresponding changes to root build.gradle. tbd about shadowjar (issue Netflix#345)

build.gradle

@@ -63,7 +63,7 @@ ext.versions = [
         rxJavaReactiveStreamsVersion : '1.+',
         scalaBinaryVersion : '2.12',
         snappyVersion : "1.1.+",
-        spectator: "1.3.+",
+        spectator: "latest.release",
         slf4j    : "1.7.0",
         testngVersion : '6.14.+',
         vavr     : "0.9.2",
@@ -129,6 +129,7 @@ ext.libraries = [
         mockitoCore3   : "org.mockito:mockito-core:${versions.mockito3}",
         mockneat       : "net.andreinc:mockneat:0.4.8",
         mqlJvm         : "io.mantisrx:mql-jvm:${versions.mqlVersion}",
+        nettyAll       : "io.netty:netty-all:${versions.nettyVersion}",
         nettyBuffer    : "io.netty:netty-buffer:${versions.nettyVersion}",
         nettyCodec     : "io.netty:netty-codec-http:${versions.nettyVersion}",
         nettyEpoll     : "io.netty:netty-transport-native-epoll:${versions.nettyVersion}:linux-x86_64",
@@ -141,6 +142,7 @@ ext.libraries = [
         slf4jLog4j12   : "org.slf4j:slf4j-log4j12:${versions.slf4j}",
         snappyJava     : "org.xerial.snappy:snappy-java:${versions.snappyVersion}",
         spectatorApi   : "com.netflix.spectator:spectator-api:${versions.spectator}",
+        spectatorExtIpc: "com.netflix.spectator:spectator-ext-ipc:${versions.spectator}",
         spectatorApi0 : "com.netflix.spectator:spectator-api:0.134.0",
         spectatorExtIpc0: "com.netflix.spectator:spectator-ext-ipc:0.134.0",
         spotifyFutures : "com.spotify:completable-futures:0.3.1",

mantis-publish/mantis-publish-netty/build.gradle

@@ -15,18 +15,13 @@
  */
 apply plugin: 'com.github.johnrengelman.shadow'
 
-ext {
-    archaiusVersion = 'latest.release'
-    spectatorVersion = 'latest.release'
-    nettyVersion = '4.1.34.Final'
-}
 
 dependencies {
     implementation project(':mantis-publish:mantis-publish-core')
-    implementation "io.netty:netty-all:$nettyVersion"
+    implementation libraries.nettyAll
 
-    implementation "com.netflix.spectator:spectator-ext-ipc:$spectatorVersion"
-    implementation "com.netflix.archaius:archaius2-core:$archaiusVersion"
+    implementation libraries.spectatorExtIpc
+    implementation libraries.archaius2Core
 
     implementation libraries.slf4jApi