fix slideshow bug, initialized slides after the content is loaded

Issue that this pull request solves

Closes: #428

Assigned a empty this.deck and initialized with new Reveal object every time ngAfterView triggers, so it assigns relevant classes after every render

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[x] Bugfix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
[ ] Documentation update (Documentation content changed)
[ ] Other (please describe):

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[x] My code follows the style guidelines of this project
[x] I have performed a self-review of my own code
[x] I have commented my code, particularly in hard-to-understand areas
[x] I have made corresponding changes to the documentation
[x] My changes generate no new warnings
[x] My changes does not break the current system and it passes all the current test cases.

Please attach the screenshots of the changes made in case of change in user interface

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