Save/Export Dialog

[simonbethke]

User story:
As user of SuperSplat I would like to see a dialog that provides options for saving and exporting splats.

Details:
Simliar to the "Load all PLY data" checkbox, a checkbox "Show save/export dialog" should be added. In case this checkbox is unchecked, the saving does not show a dialog and uses either the default settings or the last used settings.
However, with the checkbox enabled, a save/export dialog opens when saving and it initially provides these settings:

• For PLY a "Compress" checkbox
• SH Bands
• Drop-Down with default "Merge all splats" and other options are the names of the currently loaded splats
• Show the calculated file-size