Add SecondaryLink Service

[MD023]

Description

Adds new SecondaryLink service to allow generic cards to have a second link added to them in the format of an icon.

The SecondaryLink service allows generic cards to have a second link added to them in the format of an icon.

The following configuration is available for the SecondaryLink service:

- type: "SecondaryLink"
  SecondaryLinkUrl: "https://my-second-link" # url for the second link
  SecondaryLinkTarget: "_blank" # optional html tag target attribute.
  SecondaryLinkHover: "More Info" # optional text to show when the second link is hovered over.
  SecondaryLinkIcon: "fas fa-circle-info" # icon to use as the visual indicator of the link

Like the rest of Homer, FontAwesome icons can be used for the SecondaryLinkIcon.

This service was adapted from the CopyToClipboard service.

Fixes #125
Fixes #149

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• I've read & comply with the contributing guidelines
• I have tested my code for new features & regressions on both mobile & desktop devices, using the latest version of major browsers.
• I have made corresponding changes to the documentation (README.md).
• I've checked my modifications for any breaking changes, especially in the config.yml file