Update documentation

[Piotrek Koszuliński]

Trello board - ​https://trello.com/b/YfDwLj7q/13172-4-5-docs-updates

[Piotrek Koszuliński]

​http://stackoverflow.com/questions/30087440/ckeditor-4-5-0-beta-fileupload-api-issue

[Anna Tomanek]

Some more things to remember about:

1. clipboard/plugin.js file: cross-linking needed, for example between various events.
2. clipboard/plugin.js file: dataTransfer used in multiple API docs is also a bit unclear, let's either link it to something or maybe also consider writing it as normal text (data transfer object) like we do in other places.
3. Link to Toolbar Configurator in CKEditor API, most config.toolbar* entries would benefit from it.

[Olek Nowodziński]

​Webkits and default config.pasteFilter.