Make logo replaceable #1339

[MarcinAman]

In order to change a logo you need to override a logo-styles.css file with your own and in this file add the background-image property on element id='logo' like this:

#logo {
    background-image: url('https://upload.wikimedia.org/wikipedia/commons/9/9d/Ubuntu_logo.svg');
}

This would result in your page looking like this:

As not all images are created equal you may want to make some css adjustments (padding, height, width etc) to make it look nice. You should do it in logo-styles.css file.

With this PR dokka allows to add custom styles (in customStyles) and resources (in customAssets). Styles file will be added to every page as embedded resource. Styles will be added to the styles directory and assets to images.

Sample configuration can look like this:

    customStyleSheets.set(listOf(file("customResources/logo-styles.css"), file("customResources/custom-style-to-add.css")))
    customAssets.set(listOf(file("customResources/custom-resource.svg")))

[BarkingBad]

Maybe we should update user manual with info about extending custom styles and assets

[kamildoleglo]

Also you forgot to update Maven configuration