Support adding internal TeamCity libraries as a build dependency

[Rod MacKenzie]

Using a property to specify a local TeamCity installation the server and agent plugins could support adding a library not available on the TeamCity Maven repository.

In the server and agent plugin configurations an internal library could be added to the provided classpath as follows

teamcity {
    installationDir = '/path/to/TeamCity'
    server { 
        dependencies {
            library ('server-tools.jar')
        }
    }
}