Bug 36559: Add sticky table headers to transport cost matrix

Bug 36559: Add sticky table headers to transport cost matrix

To test:
1. APPLY patch and regenerate CSS. ( yarn build )
2. Have many, many branches. To test it is good to have more branches than in a standard k-t-d.
3. Go to Admin > Transport cost matrix
4. Scroll down and to the right, the table headers should stay visible.
5. Hover over any cell, a title should appear like 'Branch A / Branch B'
6. Test in Chrome and Firefox.

This uses position: sticky which has recently gained more widespread browser support:
https://caniuse.com/?search=sticky

Signed-off-by: Brendan Lawlor <blawlor@clamsnet.org>
Signed-off-by: Pedro Amorim <pedro.amorim@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>