Add updater

[dhylands]

We need an entity (this might be a task might just be a function thats called periodically) to check if updates are available, download them and apply them.

There are a variety of things that can be updated:

• The main sensorweb firmware
• TI's firmware
• The firmware for the nRF51822
• certificates for https (might require a firmware update or may just be a file update on the filesystem_

[dhylands]

@fabricedesre found this: https://github.com/cesanta/mongoose-iot/tree/master/fw/platforms/cc3200 which deals with OTA and the filesystem, so I thought I'd record the link here and make a link to #13

[tdz]

Note: [1] talks about fail-safe OTA and related APIs, workarounds, etc.

[1] http://processors.wiki.ti.com/index.php/CC32xx_Summary_of_Known_Issues#Simplelink_extlib_Changes

[tdz]

There's a PR at fabricedesre/cc3200-rs#60 that implements updating the sensorweb firmware.

[tdz]

The mentioned PR has been merged into cc3200-rs. Balrog support is being worked on.