Widths set on Blocks Everywhere in Forums breaks layout

[adamwoodnz]

Unfortunately the styles added in #201 to correct the editor width break the layout in a couple of scenarios:

1. We launched a new Forums theme which has a wider content layout, so the 620px width isn't compatible
2. On mobile devices the 620px width causes horizontal overflow (in both the old and new themes)

Screenshots

New theme desktop	New theme mobile	Old theme mobile

Suggested fix

This seems to work in all the scenarios above:

.gutenberg-support #bbpress-forums fieldset.bbp-form .blocks-everywhere {
    max-width: 100%;
    min-width: 100%;
}