Moved communication with coreClient in GameSchedulerService to DataRetriever and ApiClient classes

See merge request !16

# Conflicts:
#	core/src/main/java/cz/muni/fi/pa165/core/controller/MatchController.java
#	core/src/main/java/cz/muni/fi/pa165/core/repository/MatchRepository.java
#	core/src/main/java/cz/muni/fi/pa165/core/service/MatchService.java
#	core/src/main/resources/data.sql

Xhusarc game scheduler

See merge request !14

# Conflicts:
#	league-table/src/main/java/cz/muni/fi/pa165/leaguetable/service/TableController.java

IMPL add() and remove() HockeyPlayer to Team

CHANGE api
CHANGE tests
FIX mappers

Core test classes refactor

See merge request !12

New class diagram

See merge request !13

Xhusarc core testing

See merge request !11