"Display Image" checkbox does not always show when changing test types

[Randle Taylor]

In the Test admin section, if you change from test type Numerical to Composite the "Display Image" checkbox remains hidden. It only reappears if you switch to Upload test type. For v0.3.0 it needs to be visible for all composite test types because images can now be created via UTILS.write_file

[Ryan Bottema]

Fixed with 2c67faf