[Feature] Automatic theme-color setting

[olifre]

(originally reported as #406 )

Environment

• So Simple version: 3.2.0
• Git repository URL: https://github.com/olifre/lifelines
• GitHub Pages hosted (if yes provide URL to site): yes, https://olifre.github.io/lifelines/
• Operating system: Android, iOS, Windows Phone

Expected behavior

Theme colour for header bar is automatically adjusted with chosen "skin".

Other

I am currently using _includes/head-custom.html with content:

<!-- Chrome, Firefox OS and Opera -->
<meta name="theme-color" content="#252a34" />
<!-- Windows Phone -->
<meta name="msapplication-navbutton-color" content="#252a34" />
<!-- iOS Safari -->
<meta name="apple-mobile-web-app-status-bar-style" content="#252a34" />

It would be nice if this could be filled automatically depending on the chosen skin. You can find more details what these settings are good for (including screenshots) here, they basically control the header and status bar used by mobile devices when a page is visited:
https://stackoverflow.com/questions/26960703/how-to-change-the-color-of-header-bar-and-address-bar-in-newest-chrome-version-o
This is especially interesting if a dark theme is used for the page and the device uses a bright theme.

[olifre]

From the discussion and comment pages-themes/hacker#67 (comment) , it seems better to go with:

<!-- Chrome, Firefox OS and Opera -->
<meta name="theme-color" content="#252a34">
<!-- Windows Phone -->
<meta name="msapplication-navbutton-color" content="#252a34">
<!-- iOS Safari -->
<meta name="apple-mobile-web-app-status-bar-style" content="black-translucent">