Cascade update insert options of inherited templates

[AlenPelin]

Feature: InsertOptionsCascade

Consider 3 templates:

• T1
• T2 inherits T1
• T3 inherits T2 (and T1)

In Standard Values of each of them update Insert Options so you can insert items of same type and all derived ones:

• T1 insert options for T1
• T2 insert options for T1 and T2
• T3 insert options for T1, T2 and T3

Update insert options of T1 so that insert options also include Folder template.

Actual Result: This does not affect T2 and T3 - they still don't have Folder template in insert options.

Expected Result: All T1, T2 and T3 have Folder template in insert options

[AlenPelin]

aka InsertOptionsDelta