- clarified the fai_publication_ear prerequisites.
- changed the use of 'script' with 'command' where this makes sense.
- fixed bug in fai_wf_install=1 when running as the only ece-install
  profile. It will now set up the WF software binaries in /opt/escenic
  even if there's no other ece-install profile that installs an ECE.

- fixed bug in fai_wf_install=1 where the links to the WF software
  binaries would be wrong if the directory inside the archive was
  different from the of the name of the archive bundle itself. This is
  to workaround a bug in WF itself, see EWF-1166, but it's
  nevertheless sane hardening.

- ece-install::common_pre_install now uses
  common-bashing::ensure_variable_is_set instead of having this code
  itself. This slims off a few lines of code
- removed obsolete method ece-install::get_conf_value
- moved parsing of user input into its own method
- hardened it a wee bit
- changed ece-install::leave_trail to produce trails in
  escenic_data_dir, i.e. /var/lib/escenic/ece-install/ instead of
  /var/lib/ece-install so that it's in sync with the rest of the
  locations where ece-install writes its things.

- added trail of the newly generated Maven settings file.
- fai_wf_install=1 will no longer overwrite an existing settings.xml
  if present in root's home directory.

- cleaned up widget-framework::create_maven_settings_file a wee bit.