Backport HostedForm device data collection to v2.x

[gsmendoza]

Backport to v2.x:

• Add device data collection #116
• Fix: user should still be able to disable data collection in a SolidusBraintree hosted form #129

[gsmendoza]

As discussed in #135 (review), we're postponing this to at least SolidusBraintree 2.1. We may also want to sort out first the following concerns with device data collection:

1. Compatibility with other payment methods
2. Reuse of device data string with saved payment sources