Implemented basic front-end value formatters

(bug 56261)
This change introduces a NullFormatter as well as a formatter for the string data type to
the front-end. In order to keep the change set size small, applying the formatters will be
dealt with in a subsequent change set.

Change-Id: I10481061ac0ee925cd70b5e321153ba433cd7c26
Merge "Implemented basic front-end value formatters"