openal-soft implementation for Android
Uses the same OpenAL code as most other supported MonoGame platforms.
Supports low latency sound on Android v4.2 and above.  Devices lower than v4.2 will have higher latency on sound playback.  Android v4.4 and higher no longer require double-buffered sound on the application side.  Tested on Nexus S with v4.1.2 and Nexus 5 with v4.4.4.
Target framework version raised to v4.2 (API Level 17) in Android and Ouya projects to allow testing for low latency sound support.  Application projects should have "Compile using Android version" set to API Level 17, "Minimum Android to target" set to API Level 14 and "Target Android version" set to "Use Compile using SDK version".  This allows use of the functions to test low latency sound support (available in v4.2), but apps can still be run on v4.0 devices.
GenerateProject.xslt extracted from Protobuild.exe to allow target framework version to be changed in Android and Ouya projects and to add support for EmbeddedNativeLibrary items.

Depends on https://github.com/Mono-Game/MonoGame.Dependencies/pull/19
Merge branch 'develop' of https://github.com/mono/MonoGame into openal-soft
Updated submodule ref to get openal-soft
Removed the two Android SoundPool-based source files.
Remove OpenTK file that had been removed in prior merge to MonoGame.Dependencies.
There were two references to the removed OpenTK file.
Use device frequency and buffer size even if device reports it does not support low latency audio.  Still requires Android v4.2.
Increase max number of playing instances from 16 to 32 to match OpenAL on iOS.
Merge pull request #2750 from KonajuGames/openal-soft

openal-soft implementation for Android