[Student][RC-6.6.4] Proguard fixes (#428)

* [Student][RC-6.6.4] Proguard fixes

* add keeps for android insets

* remove unnecessary pspdfkit warnings

* Revert a few small changes, turns out the panda drawables was a local issue

* missed the import

apps/student/proguard-rules.txt

@@ -194,16 +194,12 @@
 #PSPDFKit
 -keep class com.pspdfkit.** { *; }
 -dontwarn sun.misc.**
--dontwarn com.pspdfkit.ui.PdfYouTubeActivity
--dontwarn com.pspdfkit.media.MediaGalleryView*
 -dontwarn edu.umd.cs.findbugs.annotations.SuppressWarnings
--dontwarn com.pspdfkit.configuration.PdfConfiguration
--dontwarn com.pspdfkit.configuration.activity.PdfActivityConfiguration
--dontwarn com.pspdfkit.configuration.search.SearchConfiguration
--dontwarn com.pspdfkit.signatures.Signature
--dontwarn com.pspdfkit.ui.dialog.DocumentSharingDialogConfiguration
 -keepnames class io.reactivex.android.schedulers.AndroidSchedulers
 -keepnames class io.reactivex.Observable
+-dontwarn com.pspdfkit.**
+-dontwarn android.view.WindowInsets
+-dontwarn android.graphics.Insets
 
 # Keep third party lib class names. PSPDFKit relies on those class names to be present.
 -keepnames class rx.android.schedulers.AndroidSchedulers