Improve modularity

[sveetch]

Is your feature request related to a problem? Please describe.

Currently Bireli always produces a project with DjangoCMS, Lotus and other apps.

Describe the solution you'd like

Although it is easy to disable apps from composition, there is some internal code that expect some apps like lotus or cms.

These code parts should be more flexible and should not fail when some major app is not enabled.

Describe alternatives you've considered

There is the solution to give app choices during project creation from the cookiecutter prompt, we know this is working but it involves to removes some code parts that can be useful when user want to enable major apps (like creating project without lotus would lose lotus configurations and templates).

Additional context

Add any other context or screenshots about the feature request here.