Add {% spaceless %} tags to reduce uncompressed email size

If the email body is above a certain size, Gmail trims it
and displays "[Message clipped]  View entire message" at
the end. The spaceless tag is a quick fix to reduce
HTML size a bit and allow more table rows to fit before
clipping.

templates/emails/summary-downtimes-html.html

@@ -1,5 +1,6 @@
 {% load humanize hc_extras %}
 {% regroup checks by project as groups %}
+{% spaceless %}
 <table style="margin: 0; width: 100%; font-size: 16px;" cellpadding="0" cellspacing="0">
     {% for group in groups %}
     <tr>
@@ -81,4 +82,5 @@
     {% endfor %}
     {% endfor %}
 </table>
-<br />
+<br />
+{% endspaceless %}

templates/emails/summary-html.html

@@ -1,5 +1,6 @@
 {% load humanize hc_extras %}
 {% regroup checks by project as groups %}
+{% spaceless %}
 <table style="margin: 0; width: 100%; font-size: 16px;" cellpadding="0" cellspacing="0">
     {% for group in groups %}
     <tr>
@@ -70,3 +71,4 @@
     {% endfor %}
 </table>
 <br />
+{% endspaceless %}