Editor & Viewer: Reading with auto-scroll

#### General information

* **App version:** v2.1
* **System:** v9

#### Description
Currently Markor's focus is mainly on writing and navigating text. This a task out of this years main tooic for hacktoberfest: **Reading**.

The goal of this is to add a menu toolbar button which enable auto scrolling of text.

* This should be available for both View mode (webview) and Edit mode (EditText)
* Goal is to jump every X milliseconds by a page (or e.g. 20 lines of text).
* The speed (milliseconds interval) should be configurable. Easiest is in settings.
* Dont do continous scrolling. Might look nice as showcase but not suitable for reading. (So you can focus on text with eye and it doesnt move while reading the same word :D)

Please let me know when YOU start on this, need information or any help.