Merge pull request #284 from ChrisBeaumont/echo

Extract callback property code into echo module
Merge pull request #296 from ChrisBeaumont/spectrum

Spectrum Extraction
Reorganize Doc navigation, and use astropy autodoc extensions
Remove obsolete creation_info
Fix sphinx warnings/errors in core modules
Modify pip install command on install doc. Closes #285
Update qglue guide.

Closes #163
Updated data guide
Document widget settings
Qt Documentation
Core documentation tweaks
Deploy docs with travis
Doc tweaks