Exclude exclusions in AetherExcludeResolver and add tests for handling of exclusions of unavailable artifacts

See GPRELEASE-59
triggering ConvertersConfigurationInitializer moved to spring init method
refactoring: using GrailsApplicationAware interface for grailsApplication bean injection
changing integration spec template to create class that extends IntegrationSpec class
changing integration test filename pattern to *IntegrationSpec (it wont collide with creating unit test for the same class)
use https to access Maven Central
Fix GRAILS-9834: '<g:external> : media="screen, projector" but should be media="screen, projection"'
Merge pull request #512 from candrews/GPRELEASE-59

Excluded artifacts are resolved resulting errors if they're not available
Merge pull request #530 from nobeans/GRAILS-9834-2.3.x

GRAILS-9834: '<g:external> : media="screen, projector" but should be media="screen, projection"'
Merge branch '2.3.x' into 2.4.x
Merge pull request #528 from wololock/GRAILS-11607

GRAILS-11607 grails create-integration-test should create a class extending IntegrationSpec
Merge pull request #517 from wololock/GRAILS-11116

GRAILS-11116 Custom marshaller registrar bean does not work
Merge pull request #521 from wololock/GRAILS-11631

GRAILS-11631 use https to access Maven Central
GRAILS-11631 use https connection to jcenter.bintray.com
GRAILS-11631 use https connection to grails.artifactoryonline.com (instead of http connection to repo.grails.org)
GRAILS-10166 - Add test case for embedded property query support in unit tests
Merge branch '2.3.x' into 2.4.x
GRAILS-11607 remove IntegrationSpec from artefact name given as input
Fix for GRAILS-11647 It's not possible to override collection properties with custom Hibernate UserTypes
Merge pull request #533 from lmivan/2.3.x

Fix for GRAILS-11647 It's not possible to override collection properties with custom Hibernate User types (2.3.x branch)