InfluxDBClient should dispose the child clients

[bednar]

influxdata/influxdb-client-csharp#17

Calling InfluxDBClient.close should also close a created writeApi:

InfluxDBClient influxDBClient = InfluxDBClientFactory.create(influxdbConfig.getAddress(), influxdbConfig.getToken().toCharArray());

WriteApi writeApi = influxDBClient.getWriteApi();
writeApi.writeRecord("b1", "org1", WritePrecision.NS,"h2o_feet water_level=1.0 1")

# unnecessary
writeApi.close();

influxDBClient.close();