Add support for editor-save in SelectSavegameDialog
Change editor gui to use SelectSavegameDialog instead of SaveMapDialog
Make the EditorSession save function also show a dialog to choose the map name.

This is the way the save function in spsession works.
Remove SaveMapDialog, which is now unnecessary
Refactor duplicate code
Move code showing save menu from session to gui
Remove default value for savegamename parameter in save function
Fix gettext
Move Dialog aborted check to gui code
Merge pull request #2044 from ThePawnBreak/editor-propersave

Proper saving menu for editor #1930