import: switch compat layer to use symlink-to-main-plugin method
Turns out, the old method of creating wrapping QML/JS files doesn't
allow representing a "type" (as in e.g. property <type> <var name>
).
And that's used by some applications to represent ContentTransfer
type. Switching to the symlink-to-main-plugin allows such type to be
usable by applications.
Also, adjust the QML test to specifically catch this case.
Fixes: #13 (closed)