(should be useful e.g. as input for a screen recorder)

Previously, I had expected that `enableSSL` would be set to true even if
ssl was handled through some other option (e.g. `forceSSL`).

This is apparently not the case, so the module explicitely checks for
other options as well now.

 - delete copy of example folder in picarones-elm which broke the build
 - actually check if the service should be enabled before building it

Right now, this is capable of setting up a running instance of picarones
in a couple lines of config (both backend server and the webapp, using
nginx).

More options should still be added, especially to make the backend's port
configurable (but this requires adding features to the haskell code)

to prevent noticable load times when switching slides, picarones previously
loaded all slides at once, and then only displayed whichever one was applicable.

This cause problems with larger slidesets; instead, it now loads the current
slides and the two previous and next slides (wrapping around at the end/beginning).