Allow template to use images with relative URL.
Support DOM image as well SVG image elements
Addressed issue when the node passed to normalizeRelativeUrls could be an image element.
Also:
- renamed normalizeRelativeURLs to normalizeRelativeUrls
- normalizeRelativeURLs wont filled the baseURL if not provided anymore, it's up to the called to pass it as argument
- added spec to test case were the node provided to normalizeRelativeUrls is an image element (DOM or SVG)
use constant property for the list of elements to normalize
Move constants to static properties and add cache
Merge pull request #1 from aadsm/pr-1250

Pr 1250
Merge pull request #1250 from ducarroz/relative-image

Allow template to use images with relative URL