Pass through entire path when proxying

When using the proxy blueprint a request to `/api/posts`
would send the request as `/posts` to the proxied server.
This updates the proxy blueprint to prepend the proxy base on
proxied requests.
Update changelog for http-proxy generator
Merge pull request #1874 from tstirrat/proxy-path-passthru

Pass through entire path when proxying
Add default Addon.prototype.blueprintsPath implementation.
Merge pull request #1876 from rwjblue/provide-default-addon-blueprintsPath

Add default Addon.prototype.blueprintsPath implementation.
Issue #1619 Add pod blueprint structure option for generators