Modified force.js that leverages network plugin if available

[wmathurin]

Hybrid local apps cannot do XHR calls against the server directly - so in Mobile SDK 5.0, we are introducing a new cordova plugin which does networking through the container - the code below will take advantage of the plugin if found.

Also, a number of basic methods available in forcetk.js were missing (versions, resources, describeGlobal, metadata, describe, describeLayout, queryMore and search).

NB: The file is also here: https://github.com/forcedotcom/SalesforceMobileSDK-Shared/blob/unstable/libs/force.js - ideally it should live in one repo - but there are too many references to this repo, so we decided it should be updated here as well.

@bhariharan @rwhitley @khawkins

[khawkins]

This seems fine to me. It looks like it's backward compatible with the previous version, if I didn't miss anything.