Feature/147 allow updating mimetype datastorage to solve some file type determination case

[inkhey]

related to #147.
This add the feature and add a better support for raw file determination.

[JulienPalard]

I'm not sure we can easily touch mimetype detection without first resolving #113 #114 #115 #116 #117 and #118 serie, as modifying mimetype detection will probably modify precedence of builders, and modifying precedence of builder will reveal one or many of the mentionned issues.

Also while you're touching mimetype datastorage, why not jumping directly to store (source_type, destination_type) instead of just source_type? It would help in selecting the right builder for the task, and in the future alowing to convert from A to C thrue B in case two distinct builders registered (A, B) and (B, C).

[lebouquetin]

@JulienPalard you're remark is interesting. Our strategy is the following one:

• fix the mimetypes for RAW images like @inkhey started to work on. then release a last version of preview-generator without (important) breaking changes
• start a large refactor including the storage like (source_type, destination_type) in order to deliver a preview-generator 1.x branch of development.

What do you think? Would you be interested in meeting in order to discuss about this large refactoring with @inkhey  @buxx and me?

The goal of this refactor is to convert preview-generator into a professionnal polished module (your work on preview-generator is clearly going into this direction; we also have core features refactoring required in order to achieve this goal)

[buxx]

Ok for me.