The template have some problem in "Main.cxx" and "q{xxxxxxx}MainWindow.cxx" leading to build issues

[YoungBaymax]

I used "cookiecutter gh:KitwareMedical/SlicerCustomAppTemplate" to create my app, and I did not set the Slicer_MAIN_PROJECT_APPLICATION_DISPLAY_NAME in the command line.

1. A problem shows Slicer_MAIN_PROJECT_APPLICATION_DISPLAY_NAME is not defined in Main.cxx; It may be solved by setting the value of it in command? But I solved it by changing it to Slicer_MAIN_PROJECT_APPLICATION_NAME, which is removed the substring "DISPLAY_".
2. In q{xxxxxx}AppMainWindow.cxx at line 66 reads qSlicerApplication::application()->mainApplicationDisplayName(), but there is not a attribute iin application named mainApplicationDisplayName, and I solved it by changing to mainApplicationName, which is removed the substring "Display".

[ebrahimebrahim]

This seems to be connected to #104 (@jamesobutler)

@YoungBaymax what version of Slicer is your app using? I guess it needs to be recent enough to have the changes from Slicer/Slicer#8731