Add support for Android 64 bit compilation

[ming]

Starting from Android NDK 10 (released July 2014), it added 3 new ABIs, all 64-bit: arm64-v8a, x86_64, mips64.

Currently the default target for android build is for armeabi, for other targets few changes need to be done:

1. The names of the end folders are the same as the ABI the library.

   e.g: for arm64-v8a, use lib/arm64-v8a
   

2. For ndk-build, it is necessary to define APP_ABI in the Application.mk.

   e.g: APP_ABI := arm64-v8a
   

This ticket will check to make sure that PJSIP compiles fine for those new archs.

[ming]

In 4960:

Re #1803: (Add support for Android 64 bit compilation)

[riza]

In 5056:

Re #1803: Add Application.mk which is necessary for ndk-build to define APP_ABI (needed for targets other than armeabi).