Merge branch '32-uses-default-template-for-empty-executions' into 'master'

Resolve "Add placeholder text instead of an empty string when the histogram for a query is empty"

Closes #32

See merge request !121



Merged-by: Diogo Frazão <dfrazao@gitlab.com>
Approved-by: Simon Tomlinson <stomlinson@gitlab.com>
Co-authored-by: Leonardo da Rosa <ldarosa@gitlab.com>