Fixes and conversion to new android plugin system

[pouleyKetchoupp]

I've made an update to convert your Android plugin to the new plugin system, so it has better compatibility with 3.3+ and future 4.x versions of Godot.

See funabab/godot-camera-plugin-demo#3 for the corresponding demo project update.

In the new system, .aar files are released for different versions of Godot, and users install the plugin by just copying .aar files and a configuration file in the plugin folder.

I've updated the readme to document the steps for building and for installing the plugin.

Here's a release for Godot 3.3.2:
FunababCameraPlugin-1.0.0.zip

This PR also include specific fixes to make the plugin work on recent versions (tested with Godot 3.3.2):

• Fix failure to enable the plugin when loading project due to add-on image files
• Fix camera permission request
• Fix crashes with face detection
• Fix camera preview scale (it was cropping the image before)

[Swaraj-cs]

hi, the app crashes while opening. Trying the demo and added the files in plugins folder.

logcat error:
ERROR: Condition "!singletonClass" is true. Continuing.
05-25 20:38:45.372 32406 32420 E godot : At: platform/android/java_godot_lib_jni.cpp:105:_initialize_java_modules() - Condition "!singletonClass" is true. Continuing.

Please help, I need the camera tool and this is the only one I found for 3.3.2. Really feeling bad that there is no support for camera. have to remove anything from addons?

[Swaraj-cs]

Hi, is there any option for this plugin to work with singleton?