[*] BO : Enables the browser built-in spellchecker in TinyMCE configuration

Give me my spellchecker back ! 
The browser spellchecker is disabled by defaut by TinyMCE, which is kind of awkward + TinyMCE overrides the context menu with items that are redundant as they already are in the toolbar. 
This brings the browser spellchecker and context menu back.