Directives with host: {'[class]'} in the declaration overwrites any user-defined classes

[mikerodonnell89]

Is this a bug, enhancement, or feature request?

Bug

Briefly describe your proposal

Directives do not allow the user to set any custom classes because host: {'[class]'} overwrites them. See Deno's solution for #93

What versions of Angular and Fundamental NGX? (If this is a feature request, use current version)

Angular 6.0.0, fundamental-ngx 0.0.6-beta

If this is a bug, please provide steps for reproducing it

<div class="some-class" fd-navbar-group [position]="'left'">
"some-class" is not applied to the div after rendering