[Core] Added initial support for automatic asset versioning

* An AssetVersioningStrategy can be configured within the configuration
* 2 built-in implementations are provided: ContentAssetVersioningStrategy (for fingerprinting) and FixedAssetVersioningStrategy
* The FixedAssetVersioningStrategy provides some built-in FixedVersionTypes: number, date and random
* New configuration options have been added:
** ASSET_VERSIONING to enable automatic asset versioning
** ASSET_VERSIONING_STRATEGY to select a particular strategy
** ASSET_FIXED_VERSION_TYPE to select the FixedVersionType if the FixedAssetVersioningStrategy is selected
** ASSET_FIXED_VERSION_VALUE to pass a value to the NUMBER and DATE version types
** ASSET_FIXED_VERSION_DATEFORMAT to configure the version if the version type is set to DATE
* Whatever strategy is selected, all assets loaded by the VendorBundleLoader are not affected and so are left untouched. All other assets are impacted by the versioning.
[Core] Added initial support for a new XML representation of asset bundles

* Added new strategy allowing to load XML file using a validating SAX parser
* All loaders have been updated to be able to apply 2 loading strategy sequentially : first by scanning for bundles in JSON, then XML
* The bundle name (JSON/XML) is now optional. By default, the name of the file (without extension) will be used as a bundle name

Closes #25