Commotion service manager

[dismantl]

includes https://github.com/opentechinstitute/luci-commotion-apps/pull/42
NOTE: This requires luci-commotion-apps:usability to be merged into luci-commotion-apps:master before merging
NOTE: This will also require a change to commotion-openwrt config

This will take some more extensive testing to ensure stability and functionality. I am fully available to help with the testing.

Setup:

1. Flash 2 nodes with the pull request dependencies, and at least one node with the regular nightly build.
2. record the memory usage of commotion-service-manager (CSM) upon boot.
3. Set the default app lifetime on the nodes to 1 hour (in the apps portal settings page).
4. Add 5-10 unique applications on each node (including the node(s) without CSM), meanwhile monitoring for any crashes of CSM or unusually high memory usage.

Expected results:

1. CSM should not crash (check with ps |grep commotion-service-manager)
2. CSM should not use abnormally large amounts of memory or lead to node crashes. (check with top)
3. Apps added to a node with CSM should appear almost instantly on the other node with CSM.
4. Apps on nodes with CSM should not show up on nodes without CSM, and vice versa.
5. Apps should properly expire after one hour, both on the node they were added on, as well as nodes that picked up their announcements.
6. Expired apps should no longer appear in /etc/config/applications, and their Avahi service file should have been removed from /etc/avahi/services.
7. Running kill -s USR1 $(pgrep commotion-service-manager) should result in a ;-delimited dump of service announcements in the file /tmp/local-services.out.

[dismantl]

Due to high memory usage, waiting until serval commotiond plugins are finished.