Improvements in object panel and drag/drop functionality

Objects panel drag/drop now supports multiple objects.

Object panel layer now has a new collapsible system.

Object panel tree design was improved, now it properly represents the structure.

Object panel drag/drop behavior was improved and now allows dragging after the last element.

Object panel layers now can be renamed individually.

Parent object layers now indicate if a child object is selected (even if they are collapsed).

Improvement of the way that objects are attached (parenting).

Fixed issue of transparent images being converted to JPEG when they were bigger than 2048px.

Fixed issue of grouping with CMD+G.

Fixed issue with camera aspect ratio on view resize.

Fixed issue of materials not being updated when switching between perspective/orthographic.

Fixed issue when nudging 1 px unit with arrow keys.