Change the text logo to image

[tdtgit]

This PR is for #203 , to change current text logo to <img> tag with the source image already existed in the source code.

The image width is now 38px, a little bit bigger than 36px. Let me know if it's okay.

It will look like this on:
Mobile:

Desktop:

[DokterKaj]

If you used an SVG instead of a PNG, you could theme colours of the logo like this (code from my PR #280):

<svg version="1.1" viewBox="0 0 512 512" width="38" height="38" xmlns="http://www.w3.org/2000/svg">
  <g transform="matrix(1 0 0 -1 0 512)">
    <circle cx="256" cy="256" r="256" fill="var(--outside)"/>
    <path d="M240,96 v226 h70 v-156 h58 V96 z" fill="var(--text)"/>
    <path d="M144,96 v320 h224 v-70 h-152 V96 z" fill="var(--accent)"/>
  </g>
</svg>

Not sure what colours to use though; I thought about making the circle var(--text) and the L var(--outside) but some accent colours are quite light and don't look good on a white background. The code above makes the circle the same colour as the navbar so maybe it might be better to simply remove the circle altogether.

What do you think about having the RL symbol without the circle and then "redlib" in text next to it?