On some Android versions (probably, all ones since API 15) it appears to
be impossible to catch backspace key events from system software keyboard.
Adopted a solution from
http://stackoverflow.com/questions/18581636/android-cannot-capture-backspace-delete-press-in-soft-keyboard

- Use enum for keyboard modes, 0 - no kbd, 1 - gui internal keyboard,
  2 - try system keyboard, use internal if system is unavailable

- Pass graphics object pointer to keyboard graphic module primitives to
  conform practice for similar methods.

Now system keybard is shown instead of gui_internal one always, if
it's supported by graphics module.

by graphics module.

This reverts commit 53b333a617146bc304063f8ddd0dfe2927bb6064.

That commit made POI filtering behave unexpectedly, returning empty result
sets sometimes. I was able to reproduce it on x64 linux in following way:
start POI filtering, then press "POIs" on the top to return to POI list,
then press looking glass to start POI filter once again.

I was unable to get non-empty results on my Android device.

It also has introduced some valgrind warnings about accessing an already freed
location after query text is entered and actual search is fired.

Hope @mvglasow will take a closer look on this issue.

Do the automatic switch in gui_internal_keypress_do instead of
gui_internal_search_changed so that other text input widgets would benefit,
e.g. poi search.

Setting use_overlay attr of <osd type="button"> now is supported and
enabled in default config.

There's no way to make navigation and status bar translucent nor
transparent before KITKAT, see https://developer.android.com/about/versions/android-4.4.html#UI
So corresponding code realted to SystemBarTintView should be enabled since
API 19, KITKAT.
It actually was breaking navit on my API 17 device, drawing unrelated
semitransparent bars on the top and right sides of the screen.