Cleanup autoplay logic.
[FEATURE] Allow gallery transition to be set to 'none' globally.

[Resolves #66]
[FEATURE] Add custom fade out/in transition.

[Resolves #66]
[CLEANUP] Remove unused code.
Merge pull request #69 from joelhawksley/jh/66-transition

Jh/66 transition
[FEATURE] Vertically center title slides.

[Resolves #68]