add API to manage the schedule

[yoe]

Currently, adding the schedule is done in custom Perl scripts. While that works to some extent (it doesn't have a way to detect removed talks), it's probably best if we were to have an API for people to use when editing the schedule. We might then be able to also provide a webinterface that uses that API to edit the schedule through Ajax-y things.

[yoe]

There is an sreview-import script and an SReview::Schedule Perl API to handle schedule parsing. It now also can detect removed tasks.

A REST API is still wanted.