New design for the widgets section in the docs (#866)

* Initial commit for the new widgets section

* Placing all the widgets and refining the CSS and Hugo logic

* Initial commit for the new widgets section

* Placing all the widgets and refining the CSS and Hugo logic

* Rebased and updated the info according to @verythorough contribution

* Fixing the yaml codes for the relation and select widget sections

* Merging with widgets.md and app.j

* Fixing some silly mistakes (sorry!)

* Following @verythorough contributions :)

* Adding the markdown widget and fixing the widgets container background

* Adding the URL functionality and myself as a contributor :)

* Adding myself as a contributor :)

website/site/content/docs/widgets/select.md

@@ -0,0 +1,38 @@
+---
+label: "Select"
+target: "select"
+type: "widget"
+---
+
+### Select
+
+The select widget allows you to pick a single string value from a dropdown menu.
+
+- **Name:** `select`
+- **UI:** HTML select input
+- **Data type:** string
+- **Options:**
+  - `default`: accepts a string; defaults to an empty string
+  - `options`: (**required**) a list of options for the dropdown menu; can be listed in two ways:
+      - string values: the label displayed in the dropdown is the value saved in the file
+      - object with `label` and `value` fields: the label displays in the dropdown; the value is saved in the file
+- **Example** (options as strings):
+
+  ```yaml
+  - label: "Align Content"
+    name: "align"
+    widget: "select"
+    options: ["left", "center", "right"]
+  ```
+- **Example** (options as objects):
+
+  ```yaml
+  - label: "City"
+    name: "airport-code"
+    widget: "select"
+    options:
+      - { label: "Chicago", value: "ORD" }
+      - { label: "Paris", value: "CDG" }
+      - { label: "Tokyo", value: "HND" }
+  ```
+