introduce index clustering (part 1)

In order to prevent files from getting too big and
make it easier to implement retention policies, we
are splitting all files into chunks. Each chunk
contains the data for a time interval (1 month per
default).
This first changeset introduces the ClusteredPersistentMap
that implements this for PersistentMap. It is used
for a couple (not all) of indices.

build.gradle

@@ -28,7 +28,7 @@ ext {
     lib_log4j2_core = 'org.apache.logging.log4j:log4j-core:2.11.1'
     lib_log4j2_slf4j_impl = 'org.apache.logging.log4j:log4j-slf4j-impl:2.11.1'
     
-    lib_primitive_collections='org.lucares:primitiveCollections:0.1.20181120195412'
+    lib_primitive_collections='org.lucares:primitiveCollections:0.1.20190217091430'
     
     lib_spring_boot_log4j2='org.springframework.boot:spring-boot-starter-log4j2:2.1.2.RELEASE'
     lib_spring_boot_mustache='org.springframework.boot:spring-boot-starter-mustache:2.1.2.RELEASE'
@@ -89,5 +89,5 @@ allprojects {
 }
 
 wrapper {
-    gradleVersion = '5.1.1'
+    gradleVersion = '5.2.1'
 }