UModeler Update - 2.6.17

UModeler 2.6.17 has been uploaded. Bugs reported from Discord and Unity forum have been fixed. However there are some more which are going to be handled so I'm trying to update UModeler every week for now.

Anyway the changelist of this update is as follows.

- Fix : Fixed smoothing group polygons going away after undoing. - Fix : Fixed wrong material assignment and losing mouse focus while transforming elements using a gizmo. - Fix : Fixed stopping creating the first box by dragging. This also caused losing the mouse focus. - Fix : Fixed some polygons missing after entering the game mode.