This introduces RB.Product, which contains information on the product

name, version (human-readable and raw version information), release

status, and manual URL. This can be used by the JavaScript codebase for

some purposes (like looking up the manual URL, which was previously

doable with an old constant that's now deprecated), but its main use is

for extensions.
Extensions that need to alter behavior client-side based on the version

of Review Board can now do so by reading RB.Product.versionInfo. This

can be important given the differences between Review Board 3.0 and 4.0,

particularly in the administration UI.
The information is generated once per process and then cached in-process

for future lookups.

Loaded a couple pages and verified that RB.Product was generated and

contained the correct information.