Feature/datagrid css

changed table header to bold if selected and all sortable columns are black  

- [x] finish the code
- [x] gather feedback for my changes
- [x] submit changes to the documentation


| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Tests pass?   | none
| Fixed tickets | none
| Doc           | none

based on
https://github.com/massiveart/husky/pull/147