Fixed path in Utils.asset to work with a variety of cases: absolute p…

[michielvandergeest]

Made changes to the way Utils.asset calculates the path to be more robust in various situations.

Handles paths:

• absolute paths (starting with a slash)
• relative paths (starting with dot-slash or no leading slash)
• full url (with or without protocol)

Works when served from:

• root domain
• nested directory structure