Documented pxiel/coord conversion functions (with references) for MapAdapterTile.
Remove unnecessary QLocale, QString uses POSIX-C by default.
Added missing QObject parent in constructors of helper MapAdapter classes.
Separated enum declarations from class functions.
Fixed comment usage.
Initial Layer re-organisation.

- Manage MapAdapter resources using smart shared pointers instead of
naked pointer that lead to double frees on destruction when the same
MapAdapter was used for multiple layers.