Rearrange i18n Resource files into a directory

The "app/src/processing/app" directory became mess because there are
a lot of "Resources_*.po" and "Resources_*.properties" files for the
internationalization.

Moved the resource related files into a directory "i18n" under the
"app/src/processing/app" directory.

This is for developers only. No feature changed.
Small change to "i18n_update.sh"

 * The shell should be "bash" not "sh".
 * Added an ability to update specific files only.
Sort the key of *.po files.

Without sorting the key, it is difficult to maintain the language
resource files on Git.
Applied the new utility for the ja resource.
"ja_JP" resource translation update.

 * Translated missing texts.
 * Small fixes for translation.
Merge pull request #1235 from sgk/i18nResourcesRearrange

Rearrange i18n Resource files into a directory