Fix/11

[unfor19]

Closes #11

The problem was in -

        expressions = \
            scrape_value_by_key(dashboard_body, "expr", str, []) \
            + scrape_value_by_key(dashboard_body, "query", str, [])

Previously, the function scrape_value_by_key used the default my_list=[], which caused a fixed reference to the same Python object list. Passing an empty list [] to this function sets the relevant expressions per dashboard.