Fix compatibility with Android 4.4.

The app was pretty broken on API 19, fixes:
- Remove SelectActivity card background because API 19 does not support XML SVG as bg
- Add simple folder browser for APIs without SAF
- Add simplified version of download notification
- Downgrade and replace incompatible libraries to enable SSL 1.2 on older Android versions

app/build.gradle

@@ -13,7 +13,9 @@ android {
         versionCode 2
         versionName '1.4.1'
 
+        // for SDK < 19
         multiDexEnabled true
+
         vectorDrawables {
             useSupportLibrary true
         }
@@ -105,8 +107,9 @@ dependencies {
     implementation 'com.android.support:multidex:1.0.3'
     implementation 'com.mlegy.redscreenofdeath:red-screen-of-death:0.1.3'
 
-    implementation 'com.squareup.retrofit2:retrofit:2.9.0'
-    implementation 'com.squareup.retrofit2:converter-gson:2.9.0'
+    // old version of retrofit to work with api < 21
+    implementation 'com.squareup.retrofit2:retrofit:2.6.4'
+    implementation 'com.squareup.retrofit2:converter-gson:2.6.0'
 
     coreLibraryDesugaring 'com.android.tools:desugar_jdk_libs:2.0.4'
 
@@ -117,4 +120,10 @@ dependencies {
     implementation 'com.github.bumptech.glide:annotations:4.12.0'
     implementation 'com.github.bumptech.glide:glide:4.12.0'
     implementation 'com.github.bumptech.glide:okhttp3-integration:4.12.0'
+
+    // for supporting legacy android versions:
+    implementation('com.squareup.okhttp3:okhttp:3.12.13')
+
+    implementation "androidx.multidex:multidex:2.0.1"
+    implementation 'org.conscrypt:conscrypt-android:2.5.2'
 }