Closes #22 and closes #19. Fixed height for specgrogram container, loading gif, title attribues for playback controls.
- Loading gif is just the background image behind the spectrogram, which gets covered when the spectrogram image loads.
Code review for spectroLoading branch.

 - Corrected bad default image height (255px --> 256px)
 - Moved default image height to image element (divs around image are designed to flex around image... only the image should have fixed dimensions)
 - Corrected an existing bug in the enforcedImageHeight binding - it should now work correctly (also checked, the enforcedImageHeight does override the default height created above)
Merge pull request #46 from QutBioacoustics/spectroLoading

Closes #22 and closes #19. Fixed height for specgrogram container, loadi...