Cleanup BCatalogAddOn.

* rename BCatalogAddOn to BCatalogData, since it doesn't represent an
add-on, but rather the catalog data provided by an add-on
* move BCatalogData out of Catalog.{h,cpp} into its own header and
implementation file
* drop BCatalogData::MarkForTranslation() methods, they're not needed
* drop BCatalog::GetNoAutoCollectString() methods, they're not being
used anywhere
* cleanup the B_TRANSLATE_... macros somewhat
* add versions of the B_TRANSLATE_MARK_... macros that are meant to be
used in void context (when the string isn't being used by the program,
just meant to be picked up by collectcatkeys).
* adjust several apps to use B_TRANSLATE_MARK_..._VOID where needed
* adjust users of BCatalogAddOn accordingly

Extract EditableCatalog from Catalog.{h,cpp}.

* move EditableCatalog to its own header and implementation file
* move problematic BCatalog::CatalogAddOn() to EditableCatalog
* adjust Locale tools accordingly

Cleanup BCatalogAddOn.

* rename BCatalogAddOn to BCatalogData, since it doesn't represent an
add-on, but rather the catalog data provided by an add-on
* move BCatalogData out of Catalog.{h,cpp} into its own header and
implementation file
* drop BCatalogData::MarkForTranslation() methods, they're not needed
* drop BCatalog::GetNoAutoCollectString() methods, they're not being
used anywhere
* cleanup the B_TRANSLATE_... macros somewhat
* add versions of the B_TRANSLATE_MARK_... macros that are meant to be
used in void context (when the string isn't being used by the program,
just meant to be picked up by collectcatkeys).
* adjust several apps to use B_TRANSLATE_MARK_..._VOID where needed
* adjust users of BCatalogAddOn accordingly

Extract EditableCatalog from Catalog.{h,cpp}.

* move EditableCatalog to its own header and implementation file
* move problematic BCatalog::CatalogAddOn() to EditableCatalog
* adjust Locale tools accordingly