Disable Markdown in preferences [feature-request]

If possible please add option to disable Markdown formatting completely in preferences.
It would be easier to make pure-text only notes.

e.g. I often uses pure txt lists of pros and cons like this:
- very easy to use
- resource free
- works one every webpage
- every plus (+) and minus (-) signs must be preceded with backslash () or will be converted to html lists
- every line must be ended with double spaces or it will be merged with previous line
- many non-common formatting glitches causing slowdown when taking notes

with Markdown formatting on there is much more formatting corrections (double clicks, backslashes, adding enters and double spaces, etc.)

首先定位 Firefox 扩展中的偏好设置处理和 Markdown 格式化入口。跟踪笔记的渲染方式以及偏好设置更改的应用方式。当用户可以在偏好设置中禁用 Markdown 格式化，并创建不会进行 Markdown 列表转换或相关格式修正的纯文本笔记时，即视为完成。

由索引模型根据 Issue 内容生成。