More aggregation admin work and related

- Finished updating the Appearance tab in the single item aggregation admin screen
  - Curators can now set and edit a custom aggregation-level stylesheet
  - Curator can select to use a custom home page, rather than system-generated
  - User can easily add new home pages in different languages, delete them, or edit them
  - User can upload new banner images, add new banner info in multiple languages, and remove banners
- Nearly complete with the SubCollections tab in the single item aggregation admin screen
  - Curators can now view list of subcollections, with links to view or edit the subcollections
  - Curators can now add new subcollections directly from that tab
(Still have some final things to do and then 2-3 more tabs)
- Aggregation-level change tracking
  - Added new item aggregation milestone system to track major changes to aggregations
  - Updated all aggregation procedures to auto-log and take username
  - Will add as a new screen somewhere for curators (not sure yet where)
- Front banner information encapsulated in an object, so front banner can differ per language
- Uploading a new button is now renamed correctly post-upload
- Corrected issues restricting user interface languages in nav object
Merge branch 'master' of github.com:MarkVSullivan/SobekCM-Web-Application