Replace help-blocks

[justinlittman]

They're deprecated in BS4: https://getbootstrap.com/docs/4.3/migration/#forms-1

find src -type f | xargs grep help-block
src/components/search/Search.jsx:        <span className="help-block">Sinopia search: use * as wildcard;
src/components/exports/Exports.jsx:      <p className="help-block">Exports are regenerated weekly. Each zip file contains separate files per record (as JSON-LD).</p>
src/components/load/LoadByRDFForm.jsx:          <p className="help-block">Accepts Turtle, TriG, N-Triples, N-Quads, and Notation3 (N3).</p>
src/components/load/LoadByRDFForm.jsx:          <p className="help-block">Omit brackets. If base URI is &lt;&gt;, leave blank.</p>
src/components/load/LoadByRDFForm.jsx:        <p className="help-block">This will create a new resource that can be saved in Sinopia.</p>
src/components/editor/property/InputLiteral.jsx:      {error && <span className="help-block help-block-error">{error}</span>}
src/components/editor/property/InputLookupSinopia.jsx:      <span className="help-block">Use a * to wildcard your search.</span>
src/components/editor/property/InputLookupSinopia.jsx:      {error && <span className="help-block help-block-error">{error}</span>}
src/components/editor/property/InputListLOC.jsx:      {error && <span className="help-block help-block-error">{error}</span>}
src/components/editor/property/OutlineHeader.jsx:        { error && <span className="help-block help-block-error">{error}</span>}
src/components/editor/property/InputLookupQA.jsx:      {error && <span className="help-block help-block-error">{error}</span>}
src/components/editor/property/InputURI.jsx:      {error && <span className="help-block help-block-error">{error}</span>}

[peetucket]

Note that it is possible we may also need to remove the .has-error class on form elements and decorate those elements with required, but that may require changes to the components that render the form elements, so not undertaking that here.