split up large modules into themed submodules

[mvayngrib]

right now many different utils sit in Store and utils, making it hard to know where to find things. Let's split some things up. The lowest hanging fruit are stateless utils, e.g.:

• translation-related utils (-> lib/translate.js)
• models related utils (see #20) (-> lib/models.js)
• primitives manipulation utils - strings, dates, etc. (-> lib/{string,date}.js)
• tradle primitives manipulation (getId, getCurHash, getRootHash, etc)
• promise helpers (series, batchProcess, etc.) (-> lib/promise.js)