Adjust cylinder geometry API/data storage

Store the begin/end position, rather than begin, direction and length.
This is what we used in Avogadro 1, and is often more easily reused in
other contexts.

Change-Id: Ia9a22a6f377399bd6393299ad12ca0ba1f7c5701
Merge branch 'cylinder-api'

Change-Id: I8f3b517b0d5eb9f9bc9930ac18e5a855a3842aaf
Added a basic babel command line application

This exposes the file format manager in a really basic form, and
offers the capability to translate files between supported types.
It does not output supported formats, and is probably too fragile.

Change-Id: Ic191fbe05cd5b1f1a715a5595778c63ff9501115
Merge branch 'avobabel'

Change-Id: Ie066d7a9a9f2e67c8a86d5a77b0348b21523f48d
First pass at porting POV-Ray support from Avogadro 1

Most of the basics are working, needs some testing. The lighting is
not right, and I need to add the dialog/ability to run POV-Ray from
the plugin.

Change-Id: Ib7d06f038e0ec0a0dbd71d16c4784453816925d4
Disable POV-Ray menu entry for now

It needs to save the output to a file, call POV-Ray, fix some of the
rendering artifacts.

Change-Id: I5565577f57f3cda398d3e1b8ab2a20363db1a3af
Added support for generating a movie file/GIF

This adds really rough support for generating images for a movie,
then calling the relevant command line tools to assemble the movie.
This still needs work t omake the size of the movie configurable, as
well as the location of the executables and their arguments.

Pushing this in as a work in progress, it may fail in not so obvious
ways as it also needs lots of extra error handling code too!

Change-Id: Ib2d4d4668b2356d4e3b049a22ed6bd9a064fa92e
Merge branch 'rendering-movies-rays'

Change-Id: I605780d03a86304dcdd51fdf6c2f237151c3a289