mark full import statement instead of path node

for things like no-unresolved, mark the full import when there is a problem with the path, since

- it looks bad right now in Sublime, at least (only highlights opening quote)
- semantically, if the path is not usable the whole import is botched anyway

Start by tracing the no-unresolved rule and how it selects the reported AST node for path problems. Check the current editor highlighting behavior, especially in Sublime; done means the full import statement is marked rather than only the opening quote or path node.

Written by the indexing model from the issue text.