added icons for food
stylized food selector
added app bar to page with food
sorted food elements in list picker
small refactoring
some cleanup in add food page
added page for input food prices
added settings manager
added styles for participants on food page
round button styles from another feature branch
placed buttons region for participant list on food page
add  icons for increment actions
added invisibility selector
added participant view model
update styles for participants list
food page ui improvements
and again
added icons for numeric keyboard on input price page
adapted input price page for both themes types (light and dark)
display user currency
adapted add food page for both themes types (light and dark)
saving state between navigation in scope of add food page
updated interface for participant
fix bugs with not saving selected participants and their ate coefficient on add food page
implemented multiply erase on hold erase key on numeric keyboard
added simplest validation for add food page
finished add food page
added additional appbar buttons to add food page
Merge branch 'feature/better_food_selector' into develop

Conflicts:
	Source/Foodler/App.xaml
	Source/Foodler/Common/StateManager.cs
	Source/Foodler/Models/Participant.cs
	Source/Foodler/Pages/AddFoodPage.xaml.cs
	Source/Foodler/Pages/MainPage.xaml.cs
	Source/Foodler/Resources/Images.Designer.cs
	Source/Foodler/Resources/Images.resx
	Source/Foodler/SampleData/SampleDataSource/SampleDataSource.xaml
	Source/Foodler/SampleData/SampleDataSource/SampleDataSource.xaml.cs
	Source/Foodler/SampleData/SampleDataSource/SampleDataSource.xsd
	Source/Foodler/ViewModels/AddParticipantsViewModel.cs