Refactoring work to make new folder and rename folder share

Refactoring work to make new folder and rename folder share
the same implementation (fixes NB#58817).
* src/modest-platform.h:
        * New rename_folder_dialog method.
* src/modest-ui-actions.c:
        * Now rename uses a dialog in modest platform, sharing the
          implementation with new folder dialog. Also removed old
          dialog implementation.
* src/maemo/modest-platform.c:
        * New method rename_folder_dialog, and refactored
          new_folder_dialog, creating name_folder_dialog
          that implements the same logic and controls for
          both UI actions.

pmo-trunk-r2367