Deprecated some parameters from kivy.uix.image to All Markers

[nolimitech]

Hello guys,

It's not a bug, but some parameters are being deprecated from Kivy 2.0.0. Which is annoying to receive
Based on https://kivy.org/doc/stable/api-kivy.uix.image.html

Here is the deprecated warnings:

[WARNING] Deprecated property "<BooleanProperty name=allow_stretch>" of object "<kivy_garden.mapview.view.MapMarker object at 0x000002725839F540>" was accessed, it will be removed in a future version
[WARNING] Deprecated property "<BooleanProperty name=keep_ratio>" of object "<kivy_garden.mapview.view.MapMarker object at 0x000002725839F540>" was accessed, it will be removed in a future version

To Reproduce: Just use the MapMarker, MapMArkerPopup, etc...

To remove the warnings: Inside mapview/view.py
Remove:

<MapMarker>:
    allow_stretch: True

We now use "fit_mode" with the fallowing:

• "scale-down": maintains aspect ratio without stretching.
• "fill": stretches to fill widget, may cause distortion.
• "contain": maintains aspect ratio and resizes to fit inside widget.
• "cover": maintains aspect ratio and stretches to fill widget, may clip

Hope they'll fix it soon ;)