Feature: disable non-standard bindings to standard hotkeys

Some commonly used hotkeys are re-bound. This may be good for users who mainly use codimd but disturbs others who are not used top it. Examples:

* Shift+Crtl+Cursor selects whole words
* in codimd it depends. On text it has normal behaviour, in tables it changes the column alignment
* Shift+Del usually cuts a selected text
* in codimd it cuts the current line

Idea: make an option to enable/disable this behaviour, either globally or individually per user