Bump minSdkVersion from 14 to 16

Due to TLS 1.2 implementation on the backend we need to stop supporting
Android versions lesser than 16, as the support for TLS 1.1 and 1.2 came
in JellyBean i.e. API Level 16.
Ref: https://developer.android.com/reference/javax/net/ssl/SSLSocket

OpenEdXMobile/build.gradle

@@ -265,8 +265,8 @@ android {
 
     defaultConfig {
         applicationId "org.edx.mobile"
-        // minimum version is Android 4.0
-        minSdkVersion 14
+        // minimum version is Android 4.1
+        minSdkVersion 16
         targetSdkVersion 21
 
         versionCode getVersionCode()