Use non-default config.js in samples

[wwalc]

Instead of using the config.js that is included in presets, use config.js that additionally enables the file browser (in each sample).

In short this config.js should contain what the default config contains plus this:

config.filebrowserBrowseUrl = '/apps/ckfinder/3.4.4/ckfinder.html';
config.filebrowserImageBrowseUrl = '/apps/ckfinder/3.4.4/ckfinder.html?type=Images';
config.filebrowserUploadUrl = '/apps/ckfinder/3.4.4/core/connector/php/connector.php?command=QuickUpload&type=Files';
config.filebrowserImageUploadUrl = '/apps/ckfinder/3.4.4/core/connector/php/connector.php?command=QuickUpload&type=Images';

We'll do this because we see that people try to upload images in random samples, not just in the one where we showcase the image upload feature.

Note: after adding support for it, make sure to not remove the file manager configuration from the samples that already had it enabled (file upload, paste from word etc.). The configuration there has an additional purpose of teaching users in those samples that uploading files/images is something that has to be additionally enabled.

[msamsel]

Issue should be closed with this change: https://github.com/ckeditor/ckeditor-docs/commit/40b061b683975f3768c44165b20c74ffdf2c9bc4