fixed undefined variable children_hooks + imports cleanup

[omit66]

Bugfix in function touch_import_top

current behavior:
It is not possible to create an new import without using from package.
If the parameter package of the function touch_import_top is None, the variable children_hooks is undefined.

expected behavior:
Setting package to None should create an import-statement.

changes:
children_hooks is used anyway, it should not be defined within an if-else statement.
Moved the definition.

Removed some reimports.

[lisroach]

Pinging this, we are running into this issue and would love to see it fixed.

[edschofield]

Thanks @omit66 !