Material Design Icons

[MarcHagen]

Fixes: #2755

Changed all font awesome icons and glyphicon to MDI, as close as possible.
There had been some small style changes to make it fit and look better.

As of pushing the latest version of MDI is/was 3.3.92

[jeremystretch]

While I appreciate the effort, there's a lot of questionable content here, the custom CSS you've added in particular. For example:

.mdi.mdi-magnify::before,
.mdi.mdi-close::before,
.mdi.mdi-plus::before {
    font-weight: bold;
}

Adding styling for specific icons isn't maintainable. There are also some strange rules, such as:

.mdi.mdi-fw::before {
    width: 1.2857142857142858em;
    text-align: center;
}

Further, it looks like you've included many unnecessary files from the MDI library, and omitted the version number. Ultimately it's not very practical to review a pull request with 108 changed files, even if most of them are icon name substitutions.

[MarcHagen]

Hi there,
So personally I’m never changing vendor content. Therefore I had added just the package as it is. A version number could be added to the directory name.

The icon specific formatting was just a style thing and could be removed if wished.

The ‘.mdi.mdi-fw’ is nowhere strange it exactly the same as font awesome.

For me the question is now, do you want me to change the requested changes or are you going to do it yourself, then just close this PR.

[jeremystretch]

Thank you again for the effort, but I'd like to take this on myself, and work on making icons and other UI elements more consistent overall. This will likely result in a large number of frontend tweaks spanning several releases.