ci: Rename the ci_* scripts

Give the CI scripts new names that better reflect what they do, and
make room for activities such as linting or dependency installation:
 * Rename ci_autotools.sh to ci_verify_configure.sh.
 * Rename ci_cmake.sh to ci_verify_cmake.sh.
 * Rename ci_legacy.sh to ci_verify_makefiles.sh.

Also rename CI_LEGACY_MAKEFILES to CI_MAKEFILES.

Update the config files for Travis CI and AppVeyor CI accordingly.
5 files changed