Fix copy+paste of text-on-path

When copying items to the clipboard, place them inside a group and apply any parent transforms to that group. Ungroup when pasting. This approach solves copy/paste issues with transform relationships like text-on-path and clones (replaces previous logic for clones).

Supersedes !1575 (closed)

Depends on correct implementation of grouping and ungrouping. The following issues should probably be fixed first:

• !2448 (merged) (ungrouping with shape-inside)
• !2441 (merged) (uninitialized variable for text-on-path rotation)
• #1969 (closed) (crash with LPE)

Fixes #853 (closed)