[ENG-3237][ENG-3238] Fix accessibility problems on collections submission page (#1315)

-   Tickets: 
[ENG-3237](https://openscience.atlassian.net/browse/ENG-3237)
[ENG-3238](https://openscience.atlassian.net/browse/ENG-3238)
-   Feature flag: n/a

## Purpose

Fix the accessibility problems on the Collections submission page

## Summary of Changes

1. Darken header text for each input section
2. Add aria label to search text input
3. Add aria label to search action button
4. Remove hidden label from bibliographic checkboxes
5. Add aria label to bibliographic checkboxes

## Side Effects

No, these should be isolated

## QA Notes

Functionality shouldn't be affected, only accessibility.

Author: brianjgeiger

lib/app-components/addon/components/project-contributors/list/item/styles.scss

@@ -37,11 +37,6 @@
     height: 30px;
 }
 
-.checkbox-label {
-    font-weight: normal;
-    padding-right: 5px;
-}
-
 @media (min-width: 768px) {
     .text-sm-center {
         text-align: center;

lib/app-components/addon/components/project-contributors/list/item/template.hbs

@@ -58,13 +58,12 @@
     {{! Bibliographic (Citation) }}
     <div data-test-project-contributors-list-item-citation-checkbox local-class='text-sm-center'
         class='col-xs-10 col-sm-2 col-sm-offset-0 bib-padding'>
-        <label local-class='checkbox-label' class='visible-xs-inline' for='{{@contributor.id}}-citation'>
-            <em>
-                {{t 'app_components.project_contributors.list.item.in_citation_label'}}
-            </em>
-        </label>
-        <Input @id={{concat @contributor.id '-citation'}} @type='checkbox' @disabled={{not this.canChangeBibliographic}}
-            @checked={{@contributor.bibliographic}} @change={{action @toggleBibliographic @contributor}} />
+        <Input
+            aria-label={{t 'app_components.project_contributors.list.item.in_citation_label'}}
+            @type='checkbox'
+            @disabled={{not this.canChangeBibliographic}}
+            @checked={{@contributor.bibliographic}}
+            @change={{action @toggleBibliographic @contributor}} />
     </div>
 
     {{! Remove }}

lib/app-components/addon/components/project-contributors/search/template.hbs

@@ -5,13 +5,15 @@
         class='input-group'
     >
         <Input
+            aria-label={{t 'app_components.project_contributors.search.placeholder'}}
             @class='form-control'
             @value={{this.query}}
             @placeholder={{t 'app_components.project_contributors.search.placeholder'}}
         />
         <span class='input-group-btn'>
             <button
                 data-test-project-contributors-search-button
+                aria-label={{t 'app_components.project_contributors.search.perform_search'}}
                 local-class='authors-search-button'
                 class='btn btn-default'
                 type='submit'

lib/app-components/addon/components/submit-section/active/styles.scss

@@ -1,5 +1,5 @@
 .closed {
-    color: #888;
+    color: $color-text-black;
 }
 
 .green {

translations/en-us.yml

@@ -777,6 +777,7 @@ app_components:
                 add: Add
             add_contributor_success: 'Project contributor added!'
             add_contributor_error: 'Could not add contributor.'
+            perform_search: 'Perform search'
     project_metadata:
         field_title_label: 'Title:'
         field_title_placeholder: ""