update SpringBoot to 2.1.9

Also remove direct dependencies to log4j-api and log4j-core where
possible. log4j-slf4j-impl is enough in many cases.

performanceDb/build.gradle

@@ -6,7 +6,6 @@ dependencies {
 	compile lib_jackson_databind
 	compile lib_commons_collections4
 	
-	compile lib_log4j2_api
 	compile lib_log4j2_core
 	compile lib_log4j2_slf4j_impl
 }