Support for absolute bower URLs

[sfeederle]

If bower dependencys are saved as URLs (https://bower.io/#install-packages) instead of Github shorthands the Source link in the UI breaks. This is because 'https://github.com/' is always appanded to the front of the source, even if its already a hyperlink.

This fix enables URLs in bower dependencies, even to private github enterprise servers like:

"dependencies": {
    "my-element": "https://github.customdomain.com/elements/my-element.git#^1.0.0"
}

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