App list filter UI rework

[yeriomin]

Yalp Store has been getting new features gradually. As a result, logically similar features were implemented in different, sometimes inconsistent fashion. App list filtering is one of them. Filter settings (system apps, apps with ads, paid/free apps) are currently on the preference screen and it might be unclear which pages are affected by these settings. Category filtering is, on the other hand, on the search screen.

Placing a "Filter" button in the app bar (or the main menu for older androids) would fix this inconsistency:

• filter would appear only on filterable app lists
• the overcrowded preferences screen would become smaller
• filters for which there was no place before could be implemented: rating, download count, dependencies