Sorry for the large unstructured commit. But hey, the Android code is
experimental so far.

Extract the native lo-bootstrap code into a fairly normal library
built in sal. (Previously it was the JNI part of the "Bootstrap" app.)
Just linkink normally to liblo-bootstrap from C++ code that uses it
works fine, no need to do a dlsym lookup.

Bootstrap is still a subclass of NativeActivity and can thus still be
used as an "app" (to start unit tests, or whatever), but can also be
used from some other app's Java code to just get access to the
lo-bootstrap native methods.

Introduce a new top-level "module", android, for Bootstrap and the
experiments with DocumentLoader.

Note that the experimental DocumentLoader app still crashes. It can't
create the com.sun.star.frame.Desktop instance.

I spent lots of time debugging in the painfully inadequate
ndk-gdb. (Even the newer gdb build from the "mingw-and-ndk" project is
quite crappy in many ways.) I should really experiment with
corresponding code on a normal platform first before even trying on
Android. Basically, I think that if I just can get the concept of Java
code that instantiates and uses LO components *in-process* working on
a normal desktop platform, it should work on Android, too.

potential improvements: only load the file once and use fods instead of
ods

I'm unsure on what the difference to o:Math actually is, so just make
sure the element and its contents are not ignored and each contained
m:oMath will be read in separately.