Simplify project structure

- harmonize module and directory names
- optimize Gradle settings
- remove unused Grails sample

Resolves: #1447

spring-session-samples/spring-session-sample-boot-websocket/src/main/resources/data.sql

@@ -0,0 +1,5 @@
+insert into user(id,email,password,first_name,last_name) values (0,'rob','password','Rob','Winch');
+insert into user(id,email,password,first_name,last_name) values (1,'luke','password','Luke','Taylor');
+insert into user(id,email,password,first_name,last_name) values (2,'eve','password','Luke','Taylor');
+
+update user set password = '$2a$10$FBAKClV1zBIOOC9XMXf3AO8RoGXYVYsfvUdoLxGkd/BnXEn4tqT3u';