Improve ISO references

| Q             | A
| ------------- | ---
| Doc fix?      | yes
| New docs?     | no
| Applies to    | 2.2+
| Fixed tickets | -

Fix notations according to http://www.iso.org:
* add missing space between *ISO* and the number
* *Alpha-2* > *alpha-2*

Constraints and Fields:
* *Country* & *Locale* contraint and *locale* field type: Add ISO references and Wikipedia links
* *Language* constraint: add *Unicode language identifier* hint as for the *language* field type

If anyone knows an official link to a listing of the *Unicode language identifiers*, please let me know.