Add openwrt_generic hardwarekind and cloud config implementations

[tyler-sommer]

This PR addresses #29 and #30, bringing a simple implementation for sending, receiving, and applying configuration changes to and from the Minim cloud. In addition, this adds the openwrt_generic "HardwareKind" with config handling based on UCI.

There are two pretty rough edges:

• linux_generic now depends on libcrypto, ie. openssl. This is pretty heavy for simply the MD5 function, however the curl dependency implies some sort of compatible crypto lib should be available. Right? RIght.
• linux_generic now depends on "extras" being installed too, as there is a hard reference to the "extras" generated extras.conf.sh in the linux_generic config submodule. I suppose this should be fine, albeit some more noise in the log file when the config file cant be opened-- will do more testing to make sure this is not an issue. Added a default no-op implementation as well as gracefully failing to get the config

There is also a component to this in minim-openwrt-feed, will edit with details and links.

Still need to:

• Update lists of build deps to include libcrypto
• Add a README-openwrt_generic.md
• Document the configuration applying process
• Migrate the init scripts in minim-openwrt-feed into the unum-sdk repository
• Finish updating minim-openwrt-feed
• Update install refs to include apply_conf.sh, default apply_conf.sh implementation should not depend on minim-config

Internal tasks:

• Add support in the Minim cloud for parsing the key/val format for linux_generic
• Wire up the openwrt_generic hardwarekind to use the existing UCI config parsers