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Changed getOpenMergeRequests to only retrieve the open merge requests 

Changed getOpenMergeRequests to only retrieve the open merge requests instead of retrieving all and filtering client side. This will speedup especially old projects with lots of merge requests.

Fix LICENSE typo and updated copyright years

adding permissions for project

Resolves timols/java-gitlab-api/issues/33

There is a bug in the REST API for Gitlab when retrieving commits with
pagination (https://gitlab.com/gitlab-org/gitlab-ce/issues/759). This
commit is a workaround for that - when we are retrieving commits, we
assume that the second page is numbered 1 instead of 2.

To make this not cause problems if/when the Gitlab CE project fixes the
REST API, equals() is overridden in GitlabCommit to prevent duplicate
entries.

Added method to get all commits for a project

Make integrative test run as during phase verify.

Added deleteGroup, deleteProject

Added GitlabProject support for last_activity_at and archived properties

we do not get an `401 Unauthorized` during `setup`.

Right now java-gitlab-api fails during Maven phase test when no
GITLAB instance is running on localhost.

Make this test run during `mvn verify` only and check beforehand
whether the GITLAB instance is reachable. Furthermore the
instance-under-test may be changed by adding two system properties
during invocation.

Running:
```
mvn clean verify -DTEST_TOKEN=ADMIN_TOKEN -DTEST_URL=https://GITLAB_URL
```
will pick up the values and use this instance/token.

added addGroupMemeber, deleteGroupMember, addProjectMember, deleteProjec...

prep support for https://gitlab.com/gitlab-org/gitlab-ce/issues/483

Diffs, Project Slugs and a couple other things

Added gradle wrapper

support for user CRUD