Improve way of working with Guile modules system.

* src/awget: Rename to awget.scm.  Fix usage of Guile modules.
* src/awgetd.scm, src/awlist.scm: Fix usage of Guile modules.
* src/dsv-parser.scm, src/logger.scm, src/notify-bus.scm,
  src/wget.scm: Likewise.  Rename modules.
* Makefile.am: Improve.  Install utilites such as logger and
  dsv-parser in the awget/util/ directory.  Set data dir for awget
  during install.
* Makefile.in: Update.