Unified messages for sales items

I unified all localized messages for products and services under the
key prefix "salesItem.".
Refactor JavaScript core functions

I refactor some core functions like formatNumber, parseNumber etc. in
scripts.js and move them to core.js.  Now these functions are not longer
part of the jQuery object but belong to the prototypes of the core
classes Date, Number, and String.  I also add some new functions
Number.round() and RegExp.escape().  All usages of the old jQuery core
functions are refactored.

To test these functions I add the JavaScript unit test framework QUnit
to the project substituting the old and deprecated framework JsUnit.  I
add test cases for all new core functions and place them into
"test/js/tests".
Rework Maven pom.xml

I rework the existing but incomplete pom.xml file and re-generated it by
Grails.  I reconfigure the generation of a documentation site
especially the generation of a JavaScript documentation and make it IDE
independent by using a build profile.
Refactor sales item pricing code

I move the common code for sales item pricing to the separate
salesItemPricing.gsp in grails-app/views/layouts which is included by
the product form as well as the service form.  I also optimize the
display of input errors in the pricing section and add a possibility to
remove pricing.

I also move common code to save sales items and their pricings to the
service class SalesItemService.  I fix a bug with endless dependencies
when saving domain classes by removing the foreign key in
SalesItemPricing to SalesItem.

At last, I add some unit test cases for SalesItemPricing and
SalesItemPricingItem.