Minor updates to PHPDoc blocks.

| Q             | A
| ------------- | ---
| Bug fix?      | -
| New feature?  | -
| BC breaks?    | -
| Deprecations? | -
| Tests pass?   | -
| Fixed tickets | -
| License       | -
| Doc PR        | -

In documentation block for `Adapter\ElFinder\PhpcrDriver::_fopen`, the `$write` parameter has been renamed to `$mode`, to harmonize with the code. Note: The `$mode` parameter is never used in the method implementation.
Minor changes in `MetadataInterface` and `MediaInterface` documentation blocks.