This introduces a new rbext subcommand, rbext create, which

generates a working extension source tree, complete with packaging,

based on the provided arguments. It's used to quickly get up and

running with extension development, and replaces the old, outdated

contrib/tools/generate_extension.py.
At its simplest, this just needs a human-displayable name for an

extension, and will generate a suitable package and class name from

those, and a working package and extension as well. This can be

customized with specific extension class and package names, author

information, and options for setting up static media and configuration

support. This can be expanded later for additional options, if we

choose.
There are a few major differences from the old generate_extension.py.

First, anyone with the ReviewBoard package installed can generate an

extension without needing to check out a source tree, making this much

more accessible to developers. It doesn't require an undocumented

dependency on jinja2, and instead generates all content inline within

the code (which does result in more lengthy code but helps keep all the

generation templates viewable at once). It also outputs more

future-proof extension code, unlike the old code which made use of

several deprecated Django conventions.
Documentation was added on rbext, including the existing rbext test,

and the main Extending Review Board page has a tip link that points to

rbext create.

Used this to build a few test extensions, with/without static media

and configuration. Review Board saw the extensions and let me enable

them. It also let me edit the configuration for an extension with

configuration available.
Manually inspected all the generated code.