Add config setting to change mask-icon and color.

[Nikita240]

templates/base/head.tmpl contains a hard-coded mask-icon tag and color.

<link rel="shortcut icon" href="{{AppSubUrl}}/img/favicon.png" />
<link rel="mask-icon" href="{{AppSubUrl}}/img/gitea-safari.svg" color="#609926">

This results in a bright green background when opening the repository on Chrome on Android, which doesn't match the custom theme I have at all.

We should create a config setting that allows the user to customize these parameters.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs during the next 2 weeks. Thank you for your contributions.