improve Lojban support

- Crowdin has to use the 3 letter language code, since Lojban has no 2 letter code. Added support for this in the PHP backend and renamed the translation file.
- Lojban has no plural cases, updated the plural-formulas accordingly.
- Credited the change and documented it.
- Updated the SRI hashes.

i18n/languages.json

@@ -89,7 +89,7 @@
     "ku": ["Kurdî", "Kurdish"],
     "kj": ["Kuanyama", "Kwanyama"],
     "la": ["lingua latina", "Latin"],
-    "jb": ["jbobau", "Lojban"],
+    "jbo":["jbobau", "Lojban"],
     "lb": ["Lëtzebuergesch", "Luxembourgish"],
     "lg": ["Luganda", "Ganda"],
     "li": ["Limburgs", "Limburgish"],