many improvements for redmine backlogs:

- custom CSS for jquery-ui and jquery.qtip
- restyled tooltips
- better dropdown behavior

src/sass/plugins/redmine_backlogs/jquery/jquery.qtip.scss

@@ -0,0 +1,37 @@
+@import "../common";
+
+.qtip {
+    position: absolute;
+    top: -31000px;
+    left: -31000px;
+    width: auto;
+    max-width: 500px;
+    outline: none;
+}
+
+.ui-tooltip-content {
+    position: relative;
+    padding: 10px;
+    border: 1px solid $tooltip-border;
+    background-color: $tooltip-bg;
+    color: $tooltip-text;
+    font-size: $font-size-list;
+    text-align: left;
+    word-wrap: break-word;
+    box-shadow: 0 2px 2px rgba(#000, .2);
+    overflow: hidden;
+}
+
+.ui-tooltip-tip {
+    border-color: $tooltip-border;
+    background-color: $tooltip-bg;
+}
+
+.ui-tooltip-tip {
+    position: absolute;
+    margin: 0 auto;
+    border: 0 none;
+    background: transparent;
+    overflow: hidden;
+    z-index: 10;
+}