Add android project files.

It is a verbatim copy of the project distributed along SDL.
Start with main.cpp, and enable stl and exceptions.

I started by only adding main.cpp file. I enabled all the c++ stuff that is
disabled by default in android builds. To start testing, I simlinked SDL in jni
folder.
Add all source files and some deps.

I'm putting all the deps along with sdl, but some of them don't have mk files
for Android. For now the headers are found.
Don't depend on gl.

SDL dlopens it internally when needed, or gles for android, so get rid of the
code that used gl and don't include or link to it.
Add sdl2_mixer to android.mk
Don't try to set locale in android.

I'll have to see how to substitute that. For now, ifdef'd out.
ndk doesn't like an enum as a SDL_Keycode.
No posix_memalign for android.
Remove some more unused files/code.
Fix use of transform and delete more unused files.
Link to SDL companion libs.

I took an Android.mk for sdl_gfx from
https://github.com/dailin/wesnoth_ios/blob/master/lib/SDL_gfx/Android.mk, but
compilation fails because there are some differences between SDL and SDL2. Only
those symbols are lacking for openxcom.
Update android target to 16.

Also ignored some more output from ant, as the project already builds.
android: load sdl companion libs.
android: update system settings platform specific.

I hardcoded some paths to external sd, and changed logging facilities. I'm
still not sure why writing the log file failed (segfault in log dtor).
android: only build for armeabi for now
Added support for more formats to sdl_mixer.

I also had to load the dependancies runtime. Even then, it still seems to lack
support for midi, so I kept getting 'unsupported format'. SupSuper suggested
that I could use alternative music assets, which seems to work.
android: for now hardcode locale to en-US.
Handle SDL_TEXTINPUT in TextEdit.

This is the only way to capture text in android. Together with showing the
virtual keyboard when pressing the menu button, this allows me to input text.
The unicode handling is still broken, though.
Use utf8ToWstr to support unicode again in text input.

I discovered this function which does exactly what I wanted. I don't think
using wstring internally makes much sense now, but for now it's ok.
Show vkeyboard on focus gain for text widget.

I don't think I need the auxiliary key to show the virtual keyboard. I can
automatically do that when entering input text mode. If I find any case I can
always readd it later.