Major overhaul of the roar-ng II design.

This major change is required in order to make it possible to use roar-ng II's
functionality from within the built distribution (for example, for automated
package download).

The list of changes is quite long:
  - Image construction: an external roar-ng II package is no longer needed; the
                        build script code was merged into roar-ng, so roar-ng II
                        automatically installs itself within the built
                        distribution.
  - Package search: the whole package search algorithm is smarter. An
                    additional, small package database stores the results of
                    previous package search operations and gets queried before
                    the whole package database. This speeds up package search.
                    In addition, package search is faster, because many
                    functions it consisted of were merged into one awk script.
                    Also, this script doesn't return all package entries (as in
                    the previous algorithm); instead, it finds the most
                    appropriate entry and quits.
  - Misc. changes: many small wrapper functions were removed, in order to make
                   the code shorter and easier to read.

This changes, combined with the previous commit, make it possible to build tools
based on the roar-ng II framework.