This class extends dojox.grid class and changes some methods so that the dojo Grid is adapted to fit the requirements
of PHProjekt.

It provides an own phpr.grid.Model and phpr.grid.ReadStore, which extend the corresponding classes of the dojo grid,
so that it can  handle the json Data which the PHprojekt grid receives from the server.

In addition to that it provides some methods which allows us to customize the format of specific fields within a grid:

phpr.grid.formatDate:     formatter for Date fields
phpr.grid.formatDateTime: formatter for DateTime fields
