Add the ability to update (checkbox) current template linkage during template import

Example:
1. Create template "ta".
2. Create item with key "a" in this template.
3. Full-clone this template, name it "tb".
4. Create template "tc", link it to "ta".
5. Export template "tc".
6. Update the template "tc" to be linked to "tb" (instead of "ta").
7. Attempt to import the exported XML.
Item "a" already exists on "tc", inherited from another template.

Expected result:
Link tc - > ta.