postgresql_db: add args lc_collate, lc_ctype

Allow the specification of additional locale settings (lc_collate and lc_ctype) when creating a new database (state=present).

Fail if the specified database already exists with different locale/encoding settings. (These settings can't be changed for existing databases as far as I know, and failing seems better than suggesting that no change was necessary by returning changed=False)
Merge pull request #2446 from b6d/postgresql_db-module-extension

postgresql_db: add args lc_collate, lc_ctype