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

.editorconfig

@@ -11,3 +11,6 @@ charset = utf-8
 indent_style = space
 indent_size = 4
 max_line_length=120
+
+[*.gradle]
+indent_size = 2