* Adds "Show Hidden Content Dialogue"
* Update FileBrowser.cpp
* Automatically rearrange layout to fit check boxes
* check if files are hidden in a cross platform manner
* put the hidden files checkbox below the user and factory check boxes at all times
* removed layout rearrangement code
* moved checkbox code to FileBrowser
* Removed unused include
* Cleanup in FileBrowser
Move the method `addContentCheckBox` to the other private methods.
Remove the method parameters because it can use the members.
Remove the conditional when adding the "Hidden content" checkbox because
it was always true.
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Co-authored-by: Michael Gregorius <michael.gregorius.git@arcor.de>
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