Update "default user roles" with images

[sairina]

Summary

Updated Default User Roles with images. So that the docs can visually align the user capabilities with the current UI.

For example:

Before	After

[radinamatic]

Thank you, Sairina, for you first docs contribution! :100:

PR is targeting develop, but you've added it to the 0.14 milestone. If the changes refer to Kolibri 0.14, please re-target the PR to release-v0.14.x branch.

Images

Remember that RTD is fully responsive, and that some users might read the docs on smaller screens. I believe the tab labels in the screenshot are too small to be read comfortably even on the 100% desktop browser, and even less on mobile screens.

Desktop	Mobile

Improvement suggestions:

• resize the browser window with Kolibri to as narrow as you can prior to taking the screenshot
• hover the tab label so the background color is activated (you mention the term tab in the text, but without the background it's not immediately clear where the tab is in the screenshot)

(to be continued with suggestions around tables/lists)

[sairina]

Thanks for the feedback (keep them coming)! Made the following updates:

1. Updated the images so that tabs and text are larger
2. Made sure to hover over a tab within each screenshot
3. Checked on 360x640 (MotoG4) screen (see below)

At 100% viewing on browser	On MotoG4

[radinamatic]

New images look great, thank you! :100:

I rewrote the page to remove the tables (plus some other changes), and opened a PR on your branch. If something is unclear ask away, otherwise you can just merge my PR to see the result.

[sairina]

Updated with the superadmin image. Let me know what else can be improved. Thank you for being so thorough with your comments and feedback!