packages: create UCL files for package descriptions

[ivy]

Summary

mechanically convert Makefile.package into individual UCL files for each
package and delete it.

move handling of the 'comment' and 'desc' fields from generate-ucl.sh to
template.ucl; this provides the default values for some packages which
don't have a UCL file yet.

[ivy]

fix rcmds ucl; this was converted wrong due to its different Makefile syntax.