Updated for google-cloud-monitoring and --align-period-seconds param

[rbramwell]

Overview:

• Incorporates updates from PR Fix display of data frame ingrammicro/gcpmetrics#3 (Fix display of data frame)
• Pinned package versions in requirements.txt
• Updated to use new/recommended google-cloud-monitoring package (instead of gcloud)
• Removed _build_label_filter() function and calling code, since Add support for the comparison filters of Google Monitoring API googleapis/google-cloud-python#2234 was merged and included since release 0.19.0 Cut 0.19.0 release. googleapis/google-cloud-python#2270
• Added --align-period-seconds parameter (default: 300 seconds)
• Fixed formatting in example keyfile-template.json
• Updated README.md with new parameter (example usage and added to help output)

Breaking changes:

• The default align period seconds is now 300 seconds instead of the total seconds specified by --day, --hours and --minutes parameters.