support for posting yaml app descriptors in the gui
converted *all* tabs to 4 spaces (apart from some library files), as per code review
in add-app-wizard, disable buttons when the user has to select something (template lozenge) / enter text (yaml) -- much better than hiding the buttons, as per @sjcorbett's review
Better error handling and rendering in REST and JS GUI, as per code review
Merge pull request #1130 from ahgittin/feature/yaml

post yaml apps in the gui