Add support for Gradle's software model

[Rod MacKenzie]

Add support to define TeamCity agent, server and common components using the software model.

model {
    teamcity {
        version = '9.1.6'
    }
    components {
        common(TeamCityCommonLibrarySpec) { }
        agent(TeamCityAgentLibrarySpec) { }
        server(TeamCityServerLibrarySpec) { }
    }
}

The above will compile each source set with the either the common-api, agent-api or server-api using the version defined in the teamcity block.

The agent and server plugin components will each be defined by a component spec.

model {
    components {
        agent(TeamCityAgentPluginSpec) {
            descriptor { ... }
            files { ... }
        }
        server(TeamCityServerLibrarySpec) {
            descriptor { ... }
        }
    }
}

[Rod MacKenzie]

The software model appears to be deprecated State and future of the Gradle Software Model