added keyboard shortcut help topic
corrected english translation
added test for help section keyboard shortcuts
remove first thumbnail; duplicate of big photo
removed non-english translations
images are shown in a single row and can be scrolled using buttons on sides
thumbnails scroll to currently selected image smoothly
style fixes for prev / next buttons
fixed ugly comment
inserted line breaks and wrote a test for app.views.Content.smallPhotos
Merge pull request #5102 from Faldrian/feature/4474-fix_lightbox_thumbnails

Feature/4474 fix lightbox thumbnails
Merge pull request #5100 from Faldrian/feature/add_help_keyboard_shortcuts

added keyboard shortcut help topic