Add system hook API support

Add API method for get SSH key with user information by ID of an SSH key: getSSHKey

API function was introduced by PR: https://github.com/gitlabhq/gitlabhq/pull/9591

Compilation fix

added methods:

getRawFileContent
getRawBlobContent
getFileArchive
getRepositoryTree

skip_confirmation should be null safe

Add support for project deploy keys

confirm parameter (see
http://doc.gitlab.com/ee/api/users.html#user-creation). I have chosen to
not change the meaning of the method parameter because it would break
application silently. To be discussed.

The update user doesn't have a confirm parameter so remove it: it breaks
the API but it generates a compilation error so it's easily fixable

Disconnect the HTTPURLConnection after use (Fixes #59).

As the connection is not reused, we can disconnect it right away, no need
to change the GitlabAPI API.

Added various API calls:

- block/unblock user
- update project
- transfer project to a new namespace

Dependency Upgrades

* Upgraded gradle build script

* Use gradle wrapper verion 2.4
* Plugin 'maven' added to install jar to local repo
* Sources jar will also be generated

Fix crash when deleting a project

Fix name of json property

Make getMergeRequests pull all merge requests

adding user ssh key api calls and ssh key model

Fixes for issues #44 and #45

Resolved Jackson JSON Deserialization when retrieving Projects. This fixes [Issue #45](https://github.com/timols/java-gitlab-api/issues/45).

Turned off hostname verification. Fixed [Issue #44](https://github.com/timols/java-gitlab-api/issues/44).