Add image format and source information to display (#1567)

Add image format and source information to display - needs changes to engines to actually display something. 

Displays result.source (website from which the image was taken) and result.img_format (image type and size).

Result is styled with result-format and result-source classes. See PR #1566 for an example of an engine which has the necessary changes.

Strip <span class="highlight">...</span> in the oscar image template.

searx/static/themes/courgette/css/style-rtl.css

@@ -1 +1 @@
-.q{padding:.5em 1em .5em 3em}#search_submit{left:0;right:auto}.result .favicon{float:right;margin-left:.5em;margin-right:0}#sidebar{right:auto;left:0}#results{padding:0 32px 0 272px}.search.center{padding-right:0;padding-left:17em}.right{right:auto;left:0}#pagination form+form{float:left;margin-top:-2em}.engine-table{text-align:right}
+#search_submit,#sidebar,.right{right:auto;left:0}.q{padding:.5em 1em .5em 3em}.result .favicon{float:right;margin-left:.5em;margin-right:0}#results{padding:0 32px 0 272px}.search.center{padding-right:0;padding-left:17em}#pagination form+form{float:left;margin-top:-2em}.engine-table{text-align:right}