Incorporate 3D fitting from Ahmed's masters project

[PaulHancock]

This PR will add the functionality to address #40 (fitting across multiple images), by allowing Aegean to fit across multiple frequencies at once. Users will in put a cube with two spatial and one frequency dimension, and the sources that are returned will have been fit across all frequencies with a model that includes a spectral index.

These features are work in progress, and this PR will facilitate automated testing.

TODO:

• Enable priorized fitting
• Enable blind fitting
• Figure out what to do about the data correlation across frequencies
• Update BANE to work on / produce 3d bkg/rms maps
• Allow users to have a psf that varies with frequency (define a data format)
• Figure out what annotation files will look like

[PaulHancock]

BANE now handles image cubes as intended:

• 2d images produce 2d bkg/rms maps
• 3d cube produce 3d bkg/rms maps unless you specify --slice=N in which case you'll get a 2d bkg/rms from the N'th freq band

Aegean is able to use this functionality to auto generate 3d bkg/rms images if they are not found.

[PaulHancock]

Pulled in changes that address #220 and deleted branch aeres-3d