ADD:
connection related code:
Connection/Client/Connector: Mapper,Entity
Connection: ConnectionService,ConnectionDataService
others:
eventmesh-dashboard.sql
test resources

MODIFY:
pom file: remove dependency of junit, spring-boot-starter-test contains it.
pom file: let service module depend on core module.

…che#24)

* integrate checkstyle

* fix import order & remove excessive try-catch

…che#24)

* integrate checkstyle

* fix import order & remove excessive try-catch

fixed according to PR#22 conversation
Database schema definition modified

# Conflicts:
#	eventmesh-dashboard-common/src/main/java/org/apache/eventmesh/dashboard/common/Main.java
#	eventmesh-dashboard-console/src/main/java/org/apache/eventmesh/dashboard/console/EventMeshDashboardApplication.java

add enum support for entity class.