Make it possible to translate strings to all language, by adding global function T_
Add strings to .po files
Replace all classes translations in analyser_osmosis_* by english version
Replace all classes translations in sax plugins by english version
Replace all classes translations in analyser_merge_* by english version
Add missing translations to fr.po/es.po
Regenerate translations
Add dependency on python-polib in README
Get language list from po/ directory
Don't add not translated strings to list of strings
Don't relaunch OsmoseTranslation() if it was already launched by a previous analyser
Fix issue on way of only one nodes in analyser_sax.py - we cannot get them from osmosis database
Merge branch 'i18n'

Translations for error descriptions are moved to .po files.