Upgrade Gradle and Android plugin for Gradle
Disable all signing and zip-aligning for the export templates
Give correct names to generated APKs
Put .so files built by SCons right where Gradle has to pick them according to arch & build type
Downgrade NDK platform to 14 to match minSdkVersion
using ``NotificationCompat`` in ``support-v4`` library will increase APK filesize a little bit, but it guarantees to run OK with API 4+
tested with API 19 and 23 devices
If we update build gradle to use ``compileSdkVersion 23``,
``org.apache.http`` package causes error. (issue #4711)
We need to use ``useLibrary 'org.apache.http.legacy'`` to solve this problem.
To use ``useLibrary``, we need to use latest gradle also.
And now, we faced another problem with ``APK Expansion`` java sources.
```
/platform/android/java/src/com/google/android/vending/expansion/downloader/impl/DownloadNotification.java
137 : mCurrentNotification.setLatestEventInfo(mContext, mCurrentTitle, mCurrentText, mContentIntent); // causes error
```
So, some of APK Expansion java sources are updated by referencing commits from https://github.com/danikula/Google-Play-Expansion-File
And dropped V3CustomNotification.java which was for android 3.0, since godot supports android 14 (4.0) above officially.
Unfortunately, another problem, The 'MissingTranslation' error was occurred.
So, build.gradle is updated to use ``disable 'MissingTranslation'``
Additionally, I updated ``buildToolsVersion``, ``targetSdkVersion`` to latest version.
I tested APK Expansion funtionality on Android 6.0 (Nexus 9, Nexus 6p) and Android 4.4 (Galaxy Note 2) with Google Developer console.
