switch to gradle

gradle files added
gradle: plugins added
build: files added
.travis.yml: gradle cache stored
distribution: tar and zip file stuff added
broker/build.gradle: osgi plugin added
build: bintray upload added
pom: files removed
distribution: assembly.xml removed
gradle: test ouput added to sub builds
.editorconfig: gradle files added
build: wrapper task added
osgi: added to h2_ and mapdb_storage
gradle: files cleaned
build.gradle: jars used for tar/zip

gradle/java.gradle

@@ -0,0 +1,9 @@
+apply plugin: 'java'
+apply plugin: 'jacoco'
+
+sourceCompatibility = 1.8
+targetCompatibility = 1.8
+
+tasks.withType(JavaCompile) {
+    options.encoding = 'UTF-8'
+}