Improvements to TUI for better look and consistency

Resolves:

1. #192
2. #194
3. #195
4. #198

Things noticed and done except for issues:

1. In the delegation table, the text in the cells was bold, in other tabs it was only the header, so in delegations it is now the same.
2. In the governance table, when there was only one item on the next page, it was not possible to switch to that page.
3. CheckerBoardTable now has height: 1 by default, most tables now have single-line cells.
4. Fixed the loading of data displayed on the dashboard (zero values are not shown, but loading...).