Fix paging for events commands

[mattwiller]

Both events commands were not correctly paging through the API results and writing to output. To resolve this completely, a few different things needed to be addressed:

• box events flags were adjusted to be more strict and ensure that the command always has either a stream position and limit, or a closed date-time range
• The latest box-node-sdk was pulled in, which contained a fix so the raw events JSON is returned instead of a useless iterator (since Node SDK iterators don't work with the event stream)
• box events was updated to use the raw JSON to manually page through the events results when a date range is specified (it just gives one page when a stream position is passed in, so the user can manually page if they want)
• box events:poll required a fix around how the CLI was consuming the events stream, because event emitters don't play nice with async functions

Fixes #122

[nidoran]

Lgtm!