Volume and cell number should be treated similarly

When storing cells in liquid nitrogen, we record both the volume and the number of cells within the vial. This information has the same status, just as important.

FreezerPro however treats the Standard field 'Volume' differently than the User-defined field 'Cell number'. Volume can not be changed in the same window as Cell number and both values are displayed at another part of the screen in the 2D box view. Please change this.