* use tagged containers for pkg build
* update build images
* continue to build container images in pipeline, but allow
failure (non-block)
* limit travis macos cache
* add vs2019 windows to travis
* remove xcode 9 travis build
* remove clang5/6 from CI and update min version of Clang required in
cmake
* break windows CI build into stages to reduce timeouts
* update datelib
* add if condition to travis builds to allow commit message to limit
builds by platform
* adding package signing steps for rpm and deb
* first spike at GPG signing with CI and containers
* refine ubuntu portion
* get correct gpg package version
* adding CentOS support
* fixing errors in installing gpg on ubuntu
* base64 decode the GPG key
* fixing line continuations
* revised package signing, looking for package artifacts
* add dpkg-sig to ubuntu image
* sign all deb packges
* add passphrase to GPG process
* repeat yo slef on dpkg
* sign all the rpm packages too
* install rpm-sign in the CentOS docker image
* loop through rpm files
* no need for PIN on GPG signing
FIXES: #2527
* define custom docker image for travis-linux builds based on
package build image
* add macos builds
* add windows builds (currently allowed to fail)
* improve build and shell scripts as required for the CI envs
* add asio timer latency workaround
* omit several manual tests from TravisCI which cause memory exhaustion
- Add docker container tags for "latest_BRANCH"
- Prevent different branches from overwriting deb repo artifacts
- Manual approval always required before pushing to prod
