Feature: Alternate method to supply appid

[jsphstls]

The appid is currently retrieved by regexing for a common pattern in F2 app creation files:
https://github.com/markitondemand/f2-manifest-loader/blob/master/src/index.js#L51-L52

Every file requires this pattern:

F2.Apps['com_open_f2_some_app']

The loader will extract com_open_f2_ignored_app as the appid. This works, but it creates limitations. These instances cannot currently be used:

const appId = 'com_open_f2_some_app'
F2.Apps[appId] = SomeApp

import APP_IDS from 'somewhere'
F2.Apps[APP_IDS.SOME_APP] = SomeApp

function createF2App (appId, App) {
  F2.Apps[appId] = App
}

Could a list of appIds were supplied directly to the loader?
Could the filename be used as the appId?