Ability to disable autocompletion (#512)

Ability to disable autocompletion.
3 modes:
1. Autocomplete All
2. Autocomplete All Except Collection Names
3. Autocompletion Fully Disabled
Default is Autocomplete All
```js
_scope->exec(QtUtils::toStdString(esprima), "(esprima)", true, true, true);
_scope->exec("DB.autocompleteOriginal = DB.autocomplete;", "(saveOriginalAutocomplete)", false, false, false);

if (disableCollectionAutocompletion)
    _scope->exec("DB.autocomplete = function(obj){return [];}", "", false, false, false);
```