Merge1.4

See merge request !2

only one child element will be processed of which a `tei:lem` will get precedence

fixes https://github.com/baz-ga/bazga-webapp/issues/31

add tests for date:rfc822 and improve compliance, closes #6

brought up in #2

brought up in #2 ; the $get-language-string callback now reveives a parameter with the current language code.

since it's not available within the eXistdb build artifact anymore

instead of the hard coded namespace prefix

and update functions accordingly