Snippets UI

Building on top of @dougdroper's mastalk Scribe plugin:

* Adds Snippets dropdown menu
* Adds enabled/disabled state for buttons
* Adds closeOnClick functionality to Popover component
* Adds all snippets
* Restricts inserting snippets within another tag (can only be inserted on a new line)
* Other miscellaneous improvements/fixes
Is this OK for the simple example?
```
$=table
| Equity loans            | Mortgage guarantees
|---                      |---
| New-build properties    | New-build and pre-owned properties
| Minimum 5% deposit      | Minimum 5% deposit
=$
```