Fix ImportError when an INSTALLED_APP is a dotted path to an AppConfig

[wadevries]

I have an INSTALLED_APPS setting which contains a dotted path to an AppConfig, like so:

INSTALLED_APPS = [
    # some normal apps...,
    'myproject.myapp.MyAppConfig',
    # some more apps...,
]

Somehow the import_module inside the import_crud will raise an ImportError, even though Django manages to import it as an app. If we catch the ImportError here, crudbuilder will function as normal.

Django docs on INSTALLED_APPS

[coveralls]

Coverage remained the same at 78.748% when pulling ebc64a0 on wadevries:dotted-app-import into b38c323 on asifpy:master.

[coveralls]

Coverage remained the same at 78.748% when pulling ebc64a0 on wadevries:dotted-app-import into b38c323 on asifpy:master.

[coveralls]

Coverage remained the same at 78.748% when pulling ebc64a0 on wadevries:dotted-app-import into b38c323 on asifpy:master.

[coveralls]

Coverage remained the same at 78.748% when pulling 07aecfb on wadevries:dotted-app-import into b38c323 on asifpy:master.