javadoc.opendaylight.org++ e.g. with search functionality

Once we'll have a javadoc.opendaylight.org from DOCS-33 we could see if it's L&F UX could be improved... for example, one thing I felt was really missing when I had the first look today at the big one David built from autorelease was to be able to full text search (FTS) it.

It looks Android has done work on a improving JavaDoc with a custom Doclet, see how https://developer.android.com/reference/packages.html looks like. Apparently, this is based on (their) "doclava".

There may be other JD custom CSS and Doclets worth having a look at.