Buefy: Improvement: icons in table column label

[Niels-NTG]

Overview of the problem

Buefy version: 0.7.5
Vuejs version: 2.6.10
OS/Browser: Mac OS 10.14.4/Google Chrome 74.0

Description

To indicate the type of data of a table column it is sometimes helpful to use an icon instead or in addition to label text. See image below for an example on how this could look like:

In the API b-column should get a property icon which expects a string with the name of the icon in the iconpack defined by the icon-pack property.

[jtommy]

You might use header slot (soon I'll add it in b-table-column)