Improve styling of publication, submission lists in portal

scipost_django/scipost/static/scipost/assets/css/_pool.scss

 .pool-list {
+
     > .submission {
         border: 1px solid #ddd;
         margin-bottom: 2px;

scipost_django/scipost/templates/scipost/portal/_hx_publications.html

@@ -48,7 +48,7 @@
   </div>
 </div>
 
-<h2 class="highlight mb-0">Publications{% if session_acad_field %} in {{ session_acad_field }}: {% if session_specialty %}{{ session_specialty }}{% else %}(all specialties){% endif %}{% else %} (all fields){% endif %}</h2>
+<h2 class="highlight mt-4 mb-0">Publications{% if session_acad_field %} in {{ session_acad_field }}: {% if session_specialty %}{{ session_specialty }}{% else %}(all specialties){% endif %}{% else %} (all fields){% endif %}</h2>
 
 <ul id="publications-search-results" class="list-unstyled pool-list mt-2"></ul>
 

scipost_django/scipost/templates/scipost/portal/_hx_publications_page.html

 {% for publication in page_obj %}
-  <li class="list-group-item py-2">
+  <li class="list-group-item p-2">
     {% include 'journals/_publication_li_content.html' with publication=publication %}
   </li>
 {% empty %}

scipost_django/scipost/templates/scipost/portal/_hx_submissions_base.html

@@ -29,7 +29,7 @@
   </div>
 </div>
 
-<h2 class="highlight mb-0">Submissions in {{ session_acad_field }}: {% if session_specialty %}{{ session_specialty }}{% else %}(all specialties){% endif %}</h2>
+<h2 class="highlight mt-4 mb-0">Submissions in {{ session_acad_field }}: {% if session_specialty %}{{ session_specialty }}{% else %}(all specialties){% endif %}</h2>
 
 {% if reports_needed %}
   <div class="card m-2 border-2 text-center">

scipost_django/scipost/templates/scipost/portal/_hx_submissions_page_base.html

 {% for submission in page_obj %}
-  <li class="list-group-item py-2">
+  <li class="list-group-item p-2">
     {% include 'submissions/_submission_card_content_homepage.html' with submission=submission %}
   </li>
 {% empty %}

scipost_django/scipost/templates/scipost/portal/portal.html

@@ -17,7 +17,7 @@
 
 {% block content %}
 
-  <div class="tab-content mt-4" id="portalTabContent">
+  <div class="tab-content my-2" id="portalTabContent">
 
     <div class="tab-pane portal-tab fade{% if not request.GET.tab %} show active{% endif %}"
 	 id="home"