Change header, footer and text padding based on Becs' feedback

assets/css/src/newsletter_editor/contentBlocks/footer.styl

@@ -1,6 +1,10 @@
 .mailpoet_footer_block
   padding-left: 0
   padding-right: 0
+  margin-bottom: 0
 
   .mailpoet_content
-    padding: 5px 20px
+    padding: 10px 20px
+
+    p
+      margin: 0

assets/css/src/newsletter_editor/contentBlocks/header.styl

@@ -1,6 +1,10 @@
 .mailpoet_header_block
   padding-left: 0
   padding-right: 0
+  margin-bottom: 0
 
   .mailpoet_content
-    padding: 5px 20px
+    padding: 10px 20px
+
+    p
+      margin: 0

assets/css/src/newsletter_editor/contentBlocks/text.styl

@@ -1,16 +1,21 @@
-$text-vertical-padding = 3px
-
 .mailpoet_text_block
   padding-left: 0
   padding-right: 0
 
   & > .mailpoet_content
     overflow: hidden
-    padding-top: 13px
+    padding-top: 0
-    padding-bottom: 13px
+    padding-bottom: 0px
     padding-left: 20px
     padding-right: 20px
 
+    h1, h2, h3, h4, h5, h6
+      padding: 0
+      margin: 0
+
+    p
+      margin-top: 0
+
 blockquote
   margin: 1em
   padding-left: 1em