Resolve "sample is required in `icat-store-raw`"

Closes #5 (closed)

This MR makes the sample name parameter mandatory and will prevent the error shown #5 (closed)

The behavior when sample is missing is:

icat-store-raw --beamline id00 --proposal id000000 --dataset pyicatplus_test1 --path /tmp/nothing --queue bcu-mq-04:61613
usage: icat-store-raw [-h] --beamline BEAMLINE --proposal PROPOSAL --dataset
                      DATASET --sample SAMPLE --path PATH
                      [--metadatafile METADATAFILE] [-p NAME=VALUE]
                      [--queue METADATA_URLS]
icat-store-raw: error: the following arguments are required: --sample