Dashboard: Row-specific variables

**Why is this needed**: If having a extensive dashboard with lots of variables, the variables are at the top is very cluttered and confusing. In addition to that most of the variables are used only in parts (specific rows) of the dashboard. **What would you like to be added**: I would like to have the concept of "global" and "local" dashboard variables added. "Global" variables are already in place (current ones). What would be cool if added are "local" variables which are only valid in a specific row (row-specific variables). Really nice would then be if they are located inside the row and not at the top of the dashboard. **Who is this feature for?** Anyone that uses lots of variables and anyone that likes well-structured dashboards :)