adds gzip support for press module

[jakeyr]

• add Gzip class for compression of strings and inputstreams
• modify controller to use gzip when accept-encoding header requests it
• add new gzipEnabled configuration setting to enable gzip (default off)

[dirkmc]

Hey, thanks for taking the time to add Gzip support, and share it with the community, that's great.
I hadn't added it before because I felt that it was probably best handled by the web server, rather than the application server. I'm going to merge your pull request anyway because you've made it configurable.
Could you please add a note to the documentation, and add your name to the Thanks list at the bottom as well?
Thanks!
Dirk

[jakeyr]

Yes, agreed that in most cases doing a CPU-intensive job like compression is a better job for the web server or even the LB or reverse proxy, but given that your efforts to get the core to support this at the netty level have been met with lukewarm responses, i figured we could do it here.

this spot, imo, is a good place to add gzip because when combined with a CDN using your web server as origin and the press module, you have a simple instant cached/gziped/edge-served solution. i would not recommend anyone not serving press content via a CDN turn this on, given that it's happening on every request. i'll explain as much in the doc modifications you asked for.