[enh] simple theme: RTL support

* mirror all inline SVGs so that direction SVGs display correctly on RTL
* set the bold list element in info box to RTL so the colon gets displayed on the right side
* set correct .ltr function for the left border on the search button in #q
* move text to the right in autocomplete
* move search form in lign with result article on RTL
* add the correct padding for img thumbnails in categories like music on RTL
* apply RTL to result table for map results
* align text in tables part of /preferences on RTL
* move burger menu on index page to the left on RTL
* fix positioning of drop down arrow on select boxes on RTL
* align result URL on the right (written LTR)
* align vim hotkeys help on the left since it is not translated
* image detail:
  * labels (author, format, URL, etc...) are written on the right,
    values are on the left.
  * URL are written LTR and overflow on the right

searx/static/themes/simple/src/less/style-ltr.less

@@ -0,0 +1,69 @@
+.ltr-left(@offset) {
+  left: @offset;
+}
+
+.ltr-right(@offset) {
+  right: @offset;
+}
+
+.ltr-margin-right(@offset) {
+  margin-right: @offset;
+}
+
+.ltr-margin-left(@offset) {
+  margin-left: @offset;
+}
+
+.ltr-border-right(@offset) {
+  border-right: @offset;
+}
+
+.ltr-border-left(@offset) {
+  border-left: @offset;
+}
+
+.ltr-padding-right(@offset) {
+  padding-right: @offset;
+}
+
+.ltr-padding-left(@offset) {
+  padding-left: @offset;
+}
+
+.ltr-float-left() {
+  float: left;
+}
+
+.ltr-float-right() {
+  float: right;
+}
+
+.ltr-text-align-right() {
+  text-align: right;
+}
+
+.ltr-rounded-left-corners(@radius: 10px) {
+  border-radius: @radius 0 0 @radius;
+}
+
+.ltr-rounded-right-corners(@radius: 10px) {
+  border-radius: 0 @radius @radius 0;
+}
+
+.ltr-text-align-left() {
+  text-align: left;
+}
+
+.ltr-border-left-width(@offset) {
+  border-left-width: @offset;
+}
+
+.ltr-border-right-width(@offset) {
+  border-right-width: @offset;
+}
+
+.ltr-transform() {
+  transform: scale(1, 1);
+}
+
+@import "style.less";