New function base64.encode.asset

[Baaaaaz]

Identify the Bug or Feature request

closes #2981

Description of the Change

new MT script function base64.encode.asset

Possible Drawbacks

Currently only does assets that are images.
No equivalent decode function provided as either natively handled in html (but webview performance on doing this sucks), or decoding could/should be handled via the createAsset() function instead (which may need to be adjusted to handle data URI prefixes).

Documentation Notes

new MT script function``base64.encode.asset` for converting asset images to base64, params are:

1. asset id
2. optional true/false add data URI prefix (default=false) i.e. "data:MIME type/MIME subtype;base64,"

Release Notes

New base64.encode.asset function

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This change is 

[kwvanderlinde]

Looks good. Would be nice to extend this to all assets, but I think we need a bit of extra work first on the asset management side. E.g., have Asset keep track of its detected media type so it can be used in base64.encode.asset regardless of type.