Remove/change dependency on crowd-integration-client-rest

[deepy]

The disappearance of crowd-integration-client-rest from Atlassian's maven repos means that building this plugin is now a minor headache if you haven't built it before (as you need to manually locate dependencies)

This can be seen in travis-ci (which has lost the cached dependency)

Caused by: org.apache.maven.project.DependencyResolutionException: Could not resolve dependencies for project cm.xd.sonar-plugins:sonar-crowd-plugin:sonar-plugin:2.1.3:
The following artifacts could not be resolved: com.atlassian.crowd:crowd-integration-client-rest:jar:2.7.2, com.atlassian.security:atlassian-cookie-tools:jar:3.2, com.atlassian.crowd:crowd-integration-api:jar:2.7.2: Could not transfer artifact com.atlassian.crowd:crowd-integration-client-rest:jar:2.7.2 from/to atlassian (https://packages.atlassian.com/maven-public-legacy-local): Transfer failed for https://packages.atlassian.com/maven-public-legacy-local/com/atlassian/crowd/crowd-integration-client-rest/2.7.2/crowd-integration-client-rest-2.7.2.jar