Fix #869

This PR addresses #869.
Some Notes:
- All the tests on safe_qgis.report.test and safe_qgis.widgets.test.test_dock are all passing.
- I was thinking to have this kind of behavior on all reporting system on InaSAFE. To achieve this, I need to refactor the reporting module. Refactoring that will also optimise things. I have started the implementation on another branch (refactor-report-modules). As I am not going to finish that in the near future, I made this PR.
- If this PR is merged, I will make an issue to state the above problem and implement this behavior on impact merge tools (when user chooses the template for the output). In addition to that, I will need to make an issue in inasafe-doc about updating the translation and documentation needed.
- Please test before merging this PR.