[Tests] Add UI tests to detect app crashes

[pylapp]

Today we cannot check if some tokens are defined but not implemented.

Indeed we defined a system using fatalError to make the app crash if some tokens are embedded without definitions. This is an acceptable last-chance edge case because the design system and the tokenator should manage this case before.

However we cannot know automatically if we embed such declared but not defined tokens. As a consequence we can release app which can crash, #215

We can implement simple UI unit tests so as to check if the app crashes or not. For example, the tests should, for each page, go to each view and subview. Maybe make some assertions. If the app crashes, maybe the tokens are not defined.
The tests can for example iterate on each token in the theme and check if there is a view with this token. With these tests, we will be able to check if app crashes or not, and if some tokens are missing in the display.

[pylapp]

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Such types of smoke test