[INTERNAL] grunt build publish (bower) option

grunt build --publish will update bower repositories with the build
results, create a new commit+tag and pushes it to the remote.

added placeholder replacement for ${lastchange}

bower-openui5-* repositories have to be already cloned next to the
openui5 (this) repository to get this working.

Change-Id: I497c5802df21c7497af27d3446b5db8aaafaaadd
Merge "[INTERNAL] grunt build publish (bower) option"