Add share images to instagram feed (Fixed from #79)

[LucazzP]

Add possibility to share image to Instagram feed, both iOS and Android

This PR is adding the #79 modification (Thanks @artemsivcev) and the fixes reported by @Anant00 on his PR.

I created this new ones because I saw that the other PR was inactive for a long time, so I thought doing this will reach to a next update soon.

Closes #79
Closes #81
Closes #87
Closes #43
Closes #19

[dariuspo]

@LucazzP i tried to use your forks, but got this error when sharing to instagram feed:

E/MethodChannel#social_share(22856): android.util.AndroidRuntimeException: Calling startActivity() from outside of an Activity  context requires the FLAG_ACTIVITY_NEW_TASK flag. Is this really what you want?
E/MethodChannel#social_share(22856): 	at android.app.ContextImpl.startActivity(ContextImpl.java:1018)
E/MethodChannel#social_share(22856): 	at android.app.ContextImpl.startActivity(ContextImpl.java:994)
E/MethodChannel#social_share(22856): 	at android.content.ContextWrapper.startActivity(ContextWrapper.java:403)
E/MethodChannel#social_share(22856): 	at com.shekarmudaliyar.social_share.SocialSharePlugin.onMethodCall(SocialSharePlugin.kt:86)
E/MethodChannel#social_share(22856): 	at io.flutter.plugin.common.MethodChannel$IncomingMethodCallHandler.onMessage(MethodChannel.java:262)
E/MethodChannel#social_share(22856): 	at io.flutter.embedding.engine.dart.DartMessenger.invokeHandler(DartMessenger.java:178)
E/MethodChannel#social_share(22856): 	at io.flutter.embedding.engine.dart.DartMessenger.lambda$handleMessageFromDart$0$DartMessenger(DartMessenger.java:206)
E/MethodChannel#social_share(22856): 	at io.flutter.embedding.engine.dart.-$$Lambda$DartMessenger$R4HPk6oFVb-i-YR_PN9YE6kqx1I.run(Unknown Source:12)
E/MethodChannel#social_share(22856): 	at android.os.Handler.handleCallback(Handler.java:938)
E/MethodChannel#social_share(22856): 	at android.os.Handler.dispatchMessage(Handler.java:99)
E/MethodChannel#social_share(22856): 	at android.os.Looper.loop(Looper.java:223)
E/MethodChannel#social_share(22856): 	at android.app.ActivityThread.main(ActivityThread.java:7656)
E/MethodChannel#social_share(22856): 	at java.lang.reflect.Method.invoke(Native Method)
E/MethodChannel#social_share(22856): 	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
E/MethodChannel#social_share(22856): 	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
E/flutter (22856): [ERROR:flutter/lib/ui/ui_dart_state.cc(209)] Unhandled Exception: PlatformException(error, Calling startActivity() from outside of an Activity  context requires the FLAG_ACTIVITY_NEW_TASK flag. Is this really what you want?, null, android.util.AndroidRuntimeException: Calling startActivity() from outside of an Activity  context requires the FLAG_ACTIVITY_NEW_TASK flag. Is this really what you want?

any advise?

thanks

[LucazzP]

Fixed