Make it possible to use JSF functions in the widgets field definitions

For instance when trying to reference the last documenyt contributor, the following field definition:

<field>data.dc.contributors[fn:length(data.dc.contributors)-1]</field>

is translated into "#

{row.['data.dc.contributors[fn'].length(data.dc.contributors)-1]}

" which is an invalid EL expression.

Should be translated into "#

{row.data.dc.contributors[fn:length(data.dc.contributors)-1]}

"