- Add Matrix link to header.
- Switch to [Fork-Awesome](https://forkaweso.me/Fork-Awesome/), as it
includes a matrix icon. This requires the inclusion from `header.html`
to change the otherwise hardcoded Font-Awesome style.
Reviewed-on: https://gitea.com/gitea/website/pulls/105
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-by: 6543 <6543@obermui.de>
Co-authored-by: Gusted <williamzijl7@hotmail.com>
Co-committed-by: Gusted <williamzijl7@hotmail.com>