ScheduleConfig: make the startTime and interval keys configurable

To make the ScheduleConfig better (re)usable the Config keys have
to be configurable. The default keys "startTime" and "interval"
will not be a perfect choice for every scenario. For example, if a
plugin wants to use the ScheduleConfig and have its configuration
inside a '[plugin "name"]' subsection then the "startTime" key
may be confusing:

  [plugin "name"]
    startTime = ...

as one could believe that this would be the start time of the plugin.

Change-Id: Ic4a213b08957ec7c1f4945ec5ae299bb74e82f02
2 files changed