Fix local build of onboarding-fe

Fix local build of onboarding-fe

dox-sequence-diagram-ui/package.json:
- upgrades webpack-cli to 3.3.12, the actual version 2.0.14 is not
compatible or recommended with the webpack version.

openecomp-ui/package.json:
- upgrades webpack-cli to 3.3.12, the actual version 2.0.14 is not
compatible or recommended with the webpack version.
- upgrades babel-core from 6.24.0 to 6.26.0.

Code and config fixes:
- fixes i18n openecomp-ui/src/nfvo-utils/i18n/i18n.js. The previous code
was calling an non-existent attribute of the intl-format-cache.
- fixes dox-sequence-diagram-ui path in openecomp-ui/webpack.config.js.
The previous path configuration was causing compilation problems in the
openecomp-ui (folder not found problem).

Updates README.md with used procedure to run onboarding-fe.

Change-Id: I28f7b78a1f30b5f904b3f7214f72e9741253622d
Issue-ID: SDC-3661
Signed-off-by: André Schmid <andre.schmid@est.tech>