Implement lesson slide screen

[The Figma document](https://www.figma.com/file/uLiqrlxmOB5xCppIzmiUXV/Teacher-Workout?node-id=0%3A1) contains the entire UI of the project.

You can export any image (asset) directly from Figma. [Here's how](https://drive.google.com/file/d/1KJncuAGFvKEo6zrjC9H3O59auITE0q2h/view).

**Please do not try to recreate the UI design exactly.** Prioritize using de default UI mobile components and following the [Human Interface Guidelines](https://developer.apple.com/design/human-interface-guidelines/ios). The UI objects should be positioned roughly the same as in the Figma screens.

[The mobile flow can be found in the project Wiki](https://github.com/code4romania/teacher-workout-backend/wiki/Teacher-Workout-Mobile-flow).

_Please define related colors and text & button styles in the corresponding values files. Please extract all text values in the corresponding Localizable files so we can easily adjust them. <3_

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For every lesson, we have some slides with content. For a slide, we should have the lesson title, content, optional image, options to go back, go further and close the lesson modal.
For API use our stagging environment (https://teacher.heroesof.tech/graphql).

For moving to the next step we should use GraphQL query **step** to get the next content.


TODO:

- [ ] Back should take user to the prevStep, if no prevStep is available back should be disabled
- [ ] X should close the leason, save progress and take the user to the screen where the leasson started
- [ ] Title on the top bar depends on the type of the Step (SlideStep in this case is Lectie)
- [ ] Progress is `percentComplete` from leasonStatus type

Review the linked Figma document and the Teacher Workout Mobile flow wiki, then inspect the existing iOS lesson and GraphQL integration points. Use the staging endpoint and the step query to implement the SlideStep screen, including navigation, closing and progress behavior; done means the listed TODOs work with the lesson title, content, optional image and localized styling.

Written by the indexing model from the issue text.