Change and add more features to the AutoCompleteView.

Changes:

- Suggestion was changed to an IEnumerable and AvailableSuggestion too.

New features:
- SearchHorizontalOptions
- SearchTextColor
- SearchVerticalOptions
- SuggestionsHeightRequest
- TextHorizontalOptions
- TextVerticalOptions

Note: issue related with https://github.com/XLabs/Xamarin-Forms-Labs/issues/496
Fixes last commit.