Addresses #158. Adds URL params into HTTP headers. A URL param named `KEY` with the value `VALUE` in the actual URL will appear as the header "X-Fission-Params-KEY: VALUE" in the fission function.
The poolmgr client now aggregates successive tapService() calls and sends them to the poolmgr service every 5 sec, instead of sending them immediately.
This change adds a timer trigger API, client, and implementation. Users can trigger a function with a cron-compatible string.
This change also moves the publisher interface and webhook-based publisher implementation out of kubewatcher and into a separate `publisher` package.
If no uid is provided, all versions of function files and function metadata will be deleted. If a uid is provided, only that specific version is deleted, and the "latest" version of the function moves back to the previous one.
Fixes#152
