BUG: Hide error log "threadid" column by setting model column count

If not setting the column count, the column can be hidden only after
data have been inserted. As a consequence, within the error log widget,
the column is visibility is set only after the error log model is set.
ENH: Add convenience method allowing to show/hide any error log column.
Merge branch 'fix-threadid-errorlog-column-visibility'

* fix-threadid-errorlog-column-visibility:
  ENH: Add convenience method allowing to show/hide any error log column.
  BUG: Hide error log "threadid" column by setting model column count
Extend ctkDirectoryButton to optionally filter out readOnly folders.

For details see comment associated with acceptMode property.

See also CTK issue #365

Co-authored-by: Jean-Christophe Fillion-Robin <JChris.FillionR@kitware.com>
Merge branch '365-filter-out-read-only-directory'

* 365-filter-out-read-only-directory:
  Extend ctkDirectoryButton to optionally filter out readOnly folders.