Add Translation section

Created by: mlutfy

refs #216 (closed)

Created by: mlutfy

This is a rough port of:
https://wiki.civicrm.org/confluence/display/CRMDOC/Internationalisation+for+Developers

I was hesitating whether to place this under "Framework". I guess some of it could be seen as reference docs. For me, obviously biased, translation is an important topic that needs to be top-level to have visibility, and also to have references from the various sections where it is relevant (ex: coding standards).

Created by: seancolsen

Thanks @mlutfy this is great!

I added some more improvements here and am merging now. Feel free to look over my changes and critique them, post-merge. I'm happy to revert any of my changes you're not happy with.