theme/templates/bootcamps.ics: Add iCalendar template

There are a number of unfinished issues:

* I'm waiting to see how my keep_trailing_newline patch against Jinja
  plays before dealing with the lack of a newline at the end of this
  template [1]
* I'm not sure about how to enable CR-LF newlines for a single
  template in Pelican, because Jinja normalized newlines internally.
  Maybe using CR-LF everywhere is the way to go?
* I haven't worked out non-HTML direct template installation.
  Currently `bootcamps.ics` is being installed as
  `bootcamps.ics.html`.  Fixing this might require a Pelican patch.

[1]: https://github.com/mitsuhiko/jinja2/pull/170
pelicanconf.py: Install bootcamps.ics to bootcamps.ics (not .ics.html)

Take advantage of my direct template *_SAVE_AS Pelican cleanup.