Changed the way how styles are loaded.

* File containing styles is preloaded by the editor. All
styles are available synchronously during plugins initialization.
* Thanks to styles preloading stylescombo is able to add ACRs for
its styles and to be completely hidden when all styles were rejected.
* It is now possible to prevent loading styles set file by setting
config.stylesSet = false.
Remember style only if it is allowed.
Merge branch 't/9992' into major