refactor(apis_entities): drop the apis_templatetag.html template

Drop the infamous `apis_templatetag.html` file. The included javascript
libraries where reviewed and only some of them are used.
The tooltipster library, the bootstrap-datepicker library and the
leaflet.markercluster libary are not used anywhere in the codebase and
are therefore dropped.
The remaining libraries (bootstrap-multiselect, leaflet and select2)
were moved to the base.html template to the `scriptHeader` and the
`styles` block.

apis_core/core/templates/base.html

@@ -45,19 +45,27 @@
     {% endblock favicons %}
 
     {% block styles %}
-      <link href="{% static 'css/material-symbols.css' %}" rel="stylesheet" />
-      <link href="{% static 'css/core.css' %}" rel="stylesheet" />
-      <link href="{% static 'css/E53_Place_popover.css' %}" rel="stylesheet" />
       <link rel="stylesheet"
             href="//cdnjs.cloudflare.com/ajax/libs/bootstrap-select/1.13.1/css/bootstrap-select.min.css" />
+      <link rel="stylesheet"
+            href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-multiselect/0.9.15/css/bootstrap-multiselect.css" />
+      <link rel="stylesheet"
+            href="https://cdnjs.cloudflare.com/ajax/libs/leaflet/1.3.4/leaflet.css" />
+      <link rel="stylesheet"
+            href="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.5/css/select2.min.css" />
       {% include "partials/bootstrap4_css.html" %}
+      <link href="{% static 'css/material-symbols.css' %}" rel="stylesheet" />
+      <link href="{% static 'css/core.css' %}" rel="stylesheet" />
+      <link href="{% static 'css/E53_Place_popover.css' %}" rel="stylesheet" />
     {% endblock styles %}
 
     {% block scriptHeader %}
       <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
-      <script src="{% static 'js/E53_Place_popover.js' %}"></script>
+      <script src="https://cdnjs.cloudflare.com/ajax/libs/bootstrap-multiselect/0.9.15/js/bootstrap-multiselect.min.js"></script>
+      <script src="https://cdnjs.cloudflare.com/ajax/libs/leaflet/1.3.4/leaflet.js"></script>
+      <script src="https://cdnjs.cloudflare.com/ajax/libs/select2/4.0.5/js/select2.full.min.js"></script>
       <script src="{% static "js/core.js" %}"></script>
-      {% include "apis_entities/apis_templatetag.html" %}
+      <script src="{% static 'js/E53_Place_popover.js' %}"></script>
     {% endblock %}
 
   </head>