Fix out of memory issue, when accessing the grid view

If you have collected many request data with full stacktrace,
then grid view will quickly go out of memory trying to fetch
data from all columns, even if they are not needed by the grid.

To fix that, we should explicitly say which columns we need in the collection.
Merge pull request #7 from macopedia/grid_optimization

Fix out of memory issue, when accessing the grid view