Reorganize po files into subdirectories by <lang>/ to enable transifex push

[neteler]

A successful use of the tx push command (push translations from SVN to Transifex) would require the reorganization of the PO files into subdirectories - otherwise all the languages would need to be hardcoded in the Transifex configuration (see source:grass/trunk/locale/transifex/.tx/config​). This we want to avoid to since new languages may be started on Transifex, requiring to manually update the config file every time.

Instead, after having organized the PO files into locale <lang>/ subdirectories the file_filter = ... rule [1] in the config file would start to work.

[1] ​https://docs.transifex.com/client/client-configuration

TODO:

• reorganize PO files
• update Makefile as needed
• update grass-addons/tools/transifex_merge.sh

[neteler]

In 73534:

howto_release: transifex push not yet possible, see #3539

[neteler]

In 73535:

howto_release: transifex push not yet possible, see #3539

[neteler]

In 73536:

howto_release: transifex push not yet possible, see #3539

[neteler]

Ticket retargeted after milestone closed

[martinl]

Bump milestone to 7.4.4

[neteler]

Ticket retargeted after milestone closed