Fix version number and release date in notes

Update release notes for v1.19.0

Update release notes for v1.18.0

Update release notes for v1.17.0

Update release notes for v1.16.1

Update release notes for v1.16.0

Switch to build stages on Travis CI

Add v1.15.1 to the release notes

Update changelog for 1.15.0

Updated CHANGES for 1.14.2