Improve formatting of markdown tables

[ThiefMaster]

They look pretty crappy when used e.g. in category descriptions (probably similar in minutes, haven't tested there).

Adding larger margins and/or borders between cells could be an improvement. We'd need to check if/how people currently use tables in those places (if they do at all) to make sure there are no usecases that would look worse after making a change.

|     Date    | Some Number | Other Number |
|:-----------:|:-----------:|:------------:|
| 20 Apr 2018 | 30,763       |    21,094   |
|  7 Feb 2019 | 34,751       |    23,733   |
| 12 Apr 2019 | 35,926       |    24,548   |

[TG199]

Hi @ThiefMaster I'd like to handle this.