Convert to recursive grammar format

The grammar needs to be tree-structured, this is very useful for more
complex grammars like the tumblr grammar. The generator has also been
converted to Vue, as it is faster and supports attribute directives
which looks a lot cleaner in Jade templates.

Adding words to word lists and previewing has not been implemented yet.
Use local assets due to extremely slow DNS lookups for jsdelivr
Remove most Vue warnings
Add event handlers for adding/deleting phrases in WLs
Order word lists with built-in orderBy filter
Update dummy grammar format
Add string.js string library
Implement preview functionality