Feature/save visual (#85)

- Added saving and loading to `VisualApp`
- Added pd.DataFrame support for `reco` parameter in `VisualApp`
- Corrected app classes inheritance and construction
Closes #65

Author: blondered

CHANGELOG.md

@@ -9,7 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ## Unreleased
 
 ### Added
-- VisualApp and ItemToItemVisualApp widgets for visual comparison of recommendations ([#80](https://github.com/MobileTeleSystems/RecTools/pull/80), [#82](https://github.com/MobileTeleSystems/RecTools/pull/82)) (Need examples and readme update)
+- `VisualApp` and `ItemToItemVisualApp` widgets for visual comparison of recommendations ([#80](https://github.com/MobileTeleSystems/RecTools/pull/80), [#82](https://github.com/MobileTeleSystems/RecTools/pull/82), [#85](https://github.com/MobileTeleSystems/RecTools/pull/85)) (Need examples and readme update)
 - Methods for conversion `Interactions` to raw form and for getting raw interactions from `Dataset` ([#69](https://github.com/MobileTeleSystems/RecTools/pull/69))
 - `AvgRecPopularity (Average Recommendation Popularity)` to `metrics` ([#81](https://github.com/MobileTeleSystems/RecTools/pull/81))
 - Added `normalized` parameter to `AvgRecPopularity` metric ([#89](https://github.com/MobileTeleSystems/RecTools/pull/89))

rectools/columns.py

@@ -25,6 +25,7 @@ class Columns:
     Datetime = "datetime"
     Rank = "rank"
     Score = "score"
+    Model = "model"
     UserItem = [User, Item]
     Interactions = [User, Item, Weight, Datetime]
     Recommendations = [User, Item, Score, Rank]